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Synlett 2025; 36(11): 1482-1497
DOI: 10.1055/s-0043-1775458
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First-Row Transition-Metal Catalysis For Organic Synthesis

Structural Regulation and Selective Catalysis of Biomass-Derived Carbon-Based Non-Precious Metal Nanocatalysts

Yifan Liu
a   State Key Laboratory of Photoelectric Conversion and Utilization of Solar Energy, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, P. R. of China
d   University of Chinese Academy of Sciences, Beijing 100049, P. R. of China
,
Yong Yang∗
a   State Key Laboratory of Photoelectric Conversion and Utilization of Solar Energy, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, P. R. of China
b   Shandong Energy Institute, Qingdao 266101, P. R. of China
c   Qingdao New Energy Shandong Laboratory, Qingdao 266101, P. R. of China
d   University of Chinese Academy of Sciences, Beijing 100049, P. R. of China
› Author Affiliations

This work was financially supported by the National Natural Science Foundation of China (No. 22078350) and Key Basic Research Project of Natural Science Foundation of Shandong Province (No. ZR2023ZD23).
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Abstract

In this account, we summarize our recent progress on the structural regulation and selective catalysis of biomass-derived carbon-based non-precious nanocatalysts (Fe, Co, Ni, and Cu) in organic reactions that include the selective hydrogenation of functional nitro compounds to amines, selective oxidation of alkenes, selective coupling reactions, and selective hydrogenation of unsaturated aldehydes.

1 Introduction

2 Fe-Based Catalysts

3 Co-Based Catalysts

4 Ni-Based Catalysts

5 Cu-Based Catalysts

6 Conclusions


#

Key words

biomass-derived carbon - carbon-based nanocatalyst - non-precious metal - selective catalysis - structural regulation

Biographical Sketches

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Yong Yang obtained his B.S. in 2001 from Anhui Normal University and his Ph.D. in 2006 from Xiamen University. After working at SINOPEC Shanghai Research Institute of Petrochemical Technology as an Engineer (2006–2007), he moved to a postdoctoral fellow position at The University of Tokyo (Japan) (2008–2010) and Pennsylvania State University (2011–2013). In 2013, he worked as a Senior Scientist at Institute of Chemical Engineering and Sciences, Agent of Science, Technology and Research (A*STAR) in Singapore. In 2016, he moved back to China and was appointed as a professor at Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences. His research interests focus on fabrication of non-precious metal nanocatalysts for green and sustainable organic reactions.

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Yifan Liu obtained his B.S. in 2022 from Shandong Normal University and is currently a Ph.D. student under the supervision of Prof. Yong Yang at Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences. His current research focuses on developing biomass-derived carbon-based non-precious metal nanocatalysts for selective hydrogenation transformations.

1

Introduction

To date, precious metal-based catalysts remain dominant in industrial applications; however, they face significant challenges, including low Earth abundance, high cost, and high toxicity to both the environment and human health.[1] [2] [3] [4] [5] [6] Consequently, the development of heterogeneous non-precious metal-based nanocatalysts is of great importance for advancing a sustainable chemical industry.[7–12] Over the past few decades, considerable efforts have been made to prepare supported non-precious metal nanocatalysts on various supports, such as activated carbon,[13] metal oxides,[14] SiO2,[15] and zeolite.[16] Nevertheless, challenges associated with low catalytic performance and poor stability against aggregation and sintering under the operational conditions greatly impede their practical applications.

In recent years, biomass has garnered considerable attention in the fields of carbon material science, fine chemicals, and catalysis owing to its natural renewability and sustainability.[17] [18] [19] [20] Biomass could be transformed into fuels, fine chemicals, and carbon material, particularly by utilizing waste biomass resources, thereby achieving the concept of ‘waste to treasure’.[21–23] A diverse range of biomass sources, including plants,[24–27] animals,[28] [29] [30] and microorganisms,[31] [32] [33] have been intensively explored for their transformation potential. In this context, converting biomass into carbon material or catalysts represents a significant area of research.[17] , [34] [35] [36] Various biomass feedstocks, including lignin,[37] cellulose,[38] chitosan,[39] chitin,[40] sucrose,[41] starch,[42] and other industrial or agricultural waste,[43] have been widely utilized as precursors for carbon material production. The resulting carbon materials can serve as effective supports for the preparation of heterogeneous catalysts and can also function as catalysts themselves for organic transformations and energy conversions.

In the last 10 years, our group has focused on the fabrication of non-precious metal-based nanocatalysts derived from biomass. Our objective is to synthesize carbon-based non-precious metal nanocatalysts in order to solve the challenges associated with these catalysts as mentioned earlier. We primarily chose renewable biomass, specifically bamboo shoots, as the raw material for fabricating various carbon-based non-precious metal nanocatalysts. China is the largest producer of bamboo shoots in the world, with an annual market of approximately 5 million tons. An attractive features of bamboo shoots is their nitrogen content, which comprises roughly 8% of their composition and includes proteins, amino acids, and vitamins, components not typically found in conventional biomass sources.[44] These N atoms can serve as binding sites to metal interactions and can be integrated into the carbon framework when converting it into carbon material during the conversion process into carbon material through high-temperature pyrolysis, eliminating the need for additional N sources.[45] [46] [47] [48] [49] [50] Given these unique properties, we have prepared a diverse set of non-precious metal-based nanocatalysts with tunable structural regulation through various preparation strategies. The resulting catalysts demonstrated outstanding activity, selectivity, and stability for various organic transformations.

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Figure 1 Schematic illustration of the preparation of a series of carbon-based non-precious metal nanocatalysts

This account presents a complete review of our recent works in the structural regulation and selective catalysis of biomass-derived carbon-based non-precious metal (Fe, Co, Ni, and Cu) catalysts. We will briefly outline the preparation processes of these catalysts and their applications in various organic catalytic reactions, including the selective hydrogenation of functional nitro compounds to amines, selective oxidation of alkenes, selective coupling reactions, and selective hydrogenation of unsaturated aldehydes. Our main purpose is to develop clean and efficient methods for the creation of biomass-derived carbon-based materials to achieve the high-value exploitation of biomass and to establish green, safe, and sustainable synthesis pathways for fine chemicals.


# 2

Fe-Based Catalysts

In 2017, we developed a straightforward and environmentally benign method for the first time to convert bamboo shoots into N-doped hierarchical porous carbon.[51] Specifically, fresh bamboo shoots are first sliced, dried, and crushed into powder, and then exposed to hydrothermal carbonization (HTC) at 180 °C using deionized water in a Teflon-lined stainless-steel autoclave transforming the bamboo shoots into biochar. Subsequently, the resulting biochar was pyrolyzed in a nitrogen atmosphere to produce N-doped carbon. In contrast to previous methods for preparing biomass-derived carbon materials, our approach eliminated the need for templates, chemical activation reagents, or exogenous N sources, rendering the process more sustainable and cost-effective. This N-doped carbon served as an ideal support for the uniform distribution of Pd nanoparticles, which exhibited superior catalytic activity, excellent selectivity, and enhanced stability for the selective semihydrogenation of alkynes. Based on this finding, we further expanded the method to synthesize a series of carbon-based non-precious metal nanocatalysts (Figure [1]). Our studies indicate that pyrolyzing a physical mixture of biochar and non-precious metal salts can synthesize biomass-derived carbon-based non-precious metal nanocatalysts with diverse morphologies and structures. The structure of the resultant catalyst is significantly influenced by factors such as pyrolysis temperature and duration, metal loading, and heteroatom doping, and post-treatment conditions.

Employing bamboo-shoot-derived biochar and Fe(NO3)3 as raw materials, a core-shell structured iron nanocomposite catalyst, designated Fe-Fe3C@NC-800, was synthesized through the pyrolysis of a physical mixing under 800 °C in an inert atmosphere.[52] Characterizations by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) clearly reveal that a unique core-shell structured Fe nanoparticle, with an average size of 14 nm was homogeneously distributed on the carbon matrix (Figure [2]). The core comprised a mixture of metallic Fe and Fe3C, covered by multiple layers of N-doped carbon. X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) further verified that Fe atoms reacted with N atoms on the carbon matrix to form Fe(II)-Nx sites, while simultaneously interacting with metallic Fe nanoparticles.

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Figure 2 (A) TEM and (B and C) HR-TEM images of the catalyst Fe-Fe3C@NC-800, the inset shows the size distribution of metallic Fe nanoparticles; (D) HAADF-STEM and the corresponding EDX elemental mappings of individual Fe-Fe3C@NC-800; (E) schematic illustration of the catalyst Fe-Fe3C@NC-800; and (F) XRD pattern of the catalyst Fe-Fe3C@NC-800

The catalyst Fe-Fe3C@NC-800 exhibited remarkable catalytic activity and selectivity in the oxidative coupling of amines and aldehydes for the synthesis of structurally diverse quinazolines and quinazolinones using H2O2 as a green and sustainable oxidant in water under mild conditions (Scheme [1]). Furthermore, the catalyst Fe-Fe3C@NC-800 could be readily separated and reused for several times without appreciable loss in both activity and selectivity. Control experiments indicate that the synergy between Fe-Nx sites and metallic Fe-Fe3C nanoparticles accounts for the superior activity and stability. This work not only illustrates the potential of nanostructured Fe-N-C catalysts for complex synthetic reactions but also provides an efficient catalytic method for the production of essential N-heterocycles in a cost-effective and sustainable manner.

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Scheme 1 Substrate scope for the synthesis of quinazolines and quinazolinones using the catalyst Fe-Fe3C@NC-800

The core-shell structured Fe-Fe3C@NC-800 exhibited efficient catalytic efficiency and good stability for the oxidative coupling of amines with aldehydes. However, its structural heterogeneity with the coexistence of complex metal sites, consisting of atomically dispersed Fe-Nx species and metallic Fe nanoparticles or nanoclusters, makes it difficult to identify the nature of the catalytically active sites and validate the intrinsic catalytic activity. Our continued study indicated that the structural and composition of the as-synthesized Fe-Fe3C@NC-800 can be precisely modified by a post-treatment approach, effectively addressing the issue of the structural heterogeneity. We treated the core-shell structured Fe nanocomposite catalyst Fe-Fe3C@NC-800 via acid etching under different acid concentrations and treatment durations (Figure [3]).[53] We found that the insoluble metallic Fe and Fe3C nanoparticles could be effectively removed without damaging the Fe-Nx sites. Specifically, acid-etching with 1 M H2SO4 at 60 °C for 12 hours completely eliminated the metallic Fe and Fe3C nanoparticles in the core, leaving a graphitic carbon shell structure that closely resembles the original size and shape to the core Fe/Fe3C core in the catalyst, as revealed by HR-TEM. Additionally, AC-HAADF-STEM demonstrated the presence of Fe nanoclusters (NCs) smaller than 1 nm, situated in proximity to Fe single sites (SAs) on the carbon matrix, labelled as Fe-NC-SA. In contrast, treatment of the catalyst Fe-Fe3C@NC-800 with 5 M H2SO4 at 80 °C for 24 hours resulted in an exclusive formation of Fe single-atom sites on the graphitic carbon matrix, designated Fe-SA. These findings highlighted the critical influence of post-treatment conditions on the structure and composition of the resultant catalysts. Furthermore, the structure and morphology, composition, chemical state, and local structure of Fe species were comprehensively characterized by XRD, BET, ICP-OES, Raman, XPS, and XAFS, which verified the coexistence of Fe single atoms with Fe nanoparticles and nanoclusters and exclusive Fe single atom sites as well.

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Figure 3 Illustration of the removal of NPs and NCs via an acid etching

The as-prepared catalysts Fe-NP-SA, Fe-NC-SA, and Fe-SA were employed for the aerobic oxidation of primary amines to synthesize biologically and pharmaceutically important imines.[53] The oxidation was conducted under an air atmosphere at 100 °C in water. Under identical conditions, the catalyst Fe-NP-SA displayed the lowest reaction activity, and Fe-SA demonstrated moderate catalytic performance. In contrast, the catalyst Fe-NC-SA, featuring both Fe SAs and NCs, exhibited the highest reaction activity compared to both Fe-NP-SA and Fe-SA. Control experiments and density functional theory (DFT) calculations revealed that Fe NCs and Fe single atoms located on N-doped carbon exhibited an interaction with a considerable charge transfer. This interaction benefits the adsorption of molecular O2 and the amine substrate, facilitating the selective generation of singlet oxygen, which thermodynamically promotes the formation of the key intermediate imine via hydrogen atom abstraction (HAA) with a reduced energy barrier. A set of aliphatic, aromatic, and heterocyclic primary amines could be efficiently converted into their corresponding imines, demonstrating a broad substrate scope with good compatibility of diverse functional groups (Scheme [2]). Remarkably, the catalyst Fe-NC-SA demonstrated high stability and could be successively reused 10 times with maintaining both catalytic activity and selectivity. Characterizations for the recovered catalyst Fe-NC-SA show no obvious changes in the structure, preserving the coexistence of Fe SAs and NCs with minimal Fe leaching.

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Scheme 2 Substrate scope of the oxidative coupling reaction of primary amines using the catalyst Fe-NC-SA

The introduction of extra heteroatoms has been established as an effective strategy to modulate the structure and surface properties of carbon-supported metal nanocatalyst.[54] Our continued study showed that introducing the P atom could tune the structure, morphologies, and surface properties of the bamboo-shoot-derived carbon-based Fe nanocatalyst.[55] [56] [57] For catalyst preparation, triphenylphosphine (PPh3) was used as the phosphorus source and was physically mixed with bamboo-shoot-derived biochar and Fe(NO3)3 prior to high-temperature pyrolysis at 800 °C under a nitrogen atmosphere, yielding a catalyst designated Fe@NPC-800 (Figure [4]).[55] XRD pattern and HRTEM images showed that metallic Fe nanoparticles containing Fe and/or Fe3C crystalline phases with uniform size were evenly dispersed on graphitic carbon. XPS and XAFS measurements demonstrate the formation of Fe–N, Fe–C, and Fe–Fe bonds in the catalyst, consistent with XRD and HRTEM results. In addition, the P 2p XPS spectrum identified three types of P species, that is, Fe–P, P–C, and PO4 3–, indicating successful doping of P atoms into the graphitic carbon framework and their reaction with Fe to form FePO4. The formation of FePO4 was confirmed by FT-IR experiments with the appearance of a characteristic band at 1045 cm–1. Furthermore, the Fe 2p XPS spectrum also verified the formation of FePO4. A pyridine-adsorption FT-IR experiment disclosed the presence of Lewis acid sites on the catalyst with the appearance of a characteristic peak at 1450 cm–1 due to the presence of high valence Fe in FePO4. Thus, two key Fe species, Fe-Nx and FePO4, function as oxidation and acid sites, respectively, and were simultaneously integrated within the porous carbon matrix.

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Figure 4 Schematic illustration of the bifunctional catalyst Fe@NPC-800

As a bifunctional catalyst, the catalyst Fe@NPC-800 exhibited high activity and selectivity for direct oxidative cleavage of alkenes into ketones or their oxidation into α-diketones.[55] A broad scope of alkenes could efficiently undergo the selective cleavage reaction, affording their corresponding one-carbon shorter ketones in high yields with good tolerance of various functional groups (Scheme [3]). Notably, terminal alkenes were oxidized to generate the respective aldehydes, and both 1,1-disubstituted and 1,1,2-trisubstituted alkenes can be oxidized to ketones or tertiary alcohols. Interestingly, introducing iodine anions into the reaction system led to the formation of α-diketones; a variety of alkenes, including 1,2-disubstituted aryl alkenes, aryl-alkyl alkenes, and derivatives of numerous natural products, could also be efficiently oxidized into their corresponding α-diketones (Scheme [4]). Furthermore, the catalyst Fe@NPC-800 was easily separated from the product for successive reuse and exhibited good stability for up to 6 times without significant loss of both activity and selectivity, indicating its robust stability. Mechanistic studies reveal that the direct oxidation of alkenes proceeds via the formation of an epoxide as an intermediate followed by either acid-catalyzed Meinwald rearrangement to give ketones with one carbon shorter or nucleophilic ring-opening to generate α-diketones in a cascade manner. This work presents a straightforward and effective approach for the direct oxidation synthesis of essential ketones and α-diketones from alkenes, which will play a crucial role in the synthesis of fine chemicals, medicines, agrochemicals, and materials.

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Scheme 3 Substrate scope of alkenes for the synthesis of ketones using the catalyst Fe@NPC-800

Intrigued by the bifunctional catalysis with integrating oxidation and Lewis acid dual active sites in one entity, the catalyst Fe@NPC-800 was further expanded for the direct oxidation of simple and readily available terminal alkenes for the selective synthesis of α-keto acids.[57] α-Keto acids are essential synthetic intermediates with widespread application in the synthesis of enzyme inhibitors, alkaloid, drugs, food additives, and fine chemicals. A series of terminal alkenes were smoothly converted into their corresponding α-keto acids in up to 80% yield with good tolerance of functional groups (Scheme [5]). In addition, the bifunctional Fe@NPC-800 could be easily recovered from the reaction mixture and then be reused without obvious loss of catalytic activity after successive uses. Mechanism studies indicate that the reaction proceeds in a concerted manner. Initially, the epoxide intermediate is formed via epoxidation of the terminal alkene catalyzed by Fe@NPC-800 with TBHP as the oxidant. Subsequently, the synergic process of epoxy ring-opening catalyzed by Lewis acid sites of Fe@NPC and simultaneous nucleophilic attack of the iodine anion takes place to afford intermediate A, which is converted into intermediate B via nucleophilic attack of H2O and subsequent alcohol oxidation process to yield α-keto acids. This study provides a novel efficient and environmentally friendly approach for the synthesis of α-keto acids.

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Scheme 4 Substrate scope of internal alkenes for the synthesis of α-diketones using the catalyst Fe@NPC-800

We further explored the bifunctional catalyst Fe@NPC-800 for the synthesis of α-diketones employing aldehydes and ketones as raw materials.[56] It is well known that ketones and aldehydes could be converted into α,β-unsaturated ketones via aldol or the Claisen–Schmidt condensation in the presence of a base or an acid. Our earlier study revealed that one-carbon shorter ketones were produced via the formation of an epoxide as the key intermediate from the epoxidation of internal alkenes followed by subsequent Lewis acid catalyzed Meinwald rearrangement. As such, we envisioned that the synthesis of α-diketones could be synthesized via a one-pot cascade process from easily available aldehydes and ketones catalyzed by the catalyst Fe@NPC-800 using H2O2 as the oxidant and water as a green solvent under mild conditions. A broad substrate scope across both aldehydes and ketones with good functional group tolerance were converted into α-diketones in up to 90% yield (Scheme [6]). This represents the first example of an expedient and efficient synthesis of α-diketones from simple aldehydes and ketones in a cost-effective and sustainable manner.

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Scheme 5 Substrate scope of terminal alkenes for the synthesis of α-keto acids using the catalyst Fe@NPC-800
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Scheme 6 Schematic illustration of the one-pot cascade synthesis of α-diketones from aldehydes and ketones

In addition to the introduction of P atoms into the bamboo-shoot-derived carbon-based Fe nanocatalysts, we also explored the influence of heteroatom S atom doping on the structure and catalytic activity of the resultant catalyst.[58] In this regard, the core-shell structure Fe nanocatalyst Fe-Fe3C@NC-800 was physically mixed with sulfur powder prior to high-temperature pyrolysis. Notably, the core-shell structured Fe-Fe3C@NC-800 underwent reconstruction during high-temperature pyrolysis, transforming from the core-shell structured metallic Fe/Fe3C nanoparticles to form single-phase pyrite FeS2 nanoparticles that were labelled as FeS2/NSC (Figure [5]). XPS analysis revealed that S atoms were doped into the graphitic carbon framework, forming C–S–C bonds. Comprehensive characterizations, including XRD, Raman, BET, HR-TEM, XPS, and Mössbauer spectroscopy revealed that single-phase pyrite FeS2 nanoparticles had a precisely defined composition and uniform size, homogeneously dispersed on N,S-codoped porous carbon with large specific surface area, hierarchical porous channels, and high pore volume.

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Figure 5 Schematic illustration of the single-phase pyrite FeS2/NSC
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Figure 6 Illustration of hydrogenation of functionalized nitrobenzenes

The resulting catalyst FeS2/NSC demonstrated good catalytic activity for hydrogenation of functionalized nitroarenes with good tolerance of various functional groups in water as a sustainable and green solvent. Compared to bulk pyrite FeS2 and other non-noble metal-based heterogeneous catalysts reported in the literature, this catalyst exhibited significantly enhanced activity under mild reaction conditions. More importantly, FeS2/NSC displayed exclusive chemoselectivity for the reduction of nitro groups in challenging nitroarenes bearing varying readily reducible groups (Figure [6]). Attenuated total reflection (ATR)-IR spectra for the adsorption of nitrobenzene and styrene on FeS2/NSC showed a preferential adsorption of the nitro group on the surface, with no observation of any characteristic stretchings of the C=C bond. DFT calculations suggest that the positively charged FeS2 nanoparticles greatly enhance adsorption of the nitro group due to the large electronegative N and S atoms co-incorporated in the carbon, in line with the ATR-IR result. Moreover, this catalyst displays good recyclability after several uses, maintains steady catalytic activity, and demonstrates great practical application possibilities.


# 3

Co-Based Catalysts

The search for active, inexpensive, and stable heterogeneous catalysts for organic transformations is essential yet remains challenging.[2] Building on insight from bamboo-shoot-derived carbon-based Fe nanocatalysts, we have developed cobalt nanocomposites on N-doped hierarchical porous carbon with tunable structures for various organic reactions.[44] , [59] [60] [61] Specifically, a mixture of bamboo-shoot-derived biochar and CoCl2 was pyrolyzed under a N2 atmosphere at 700, 800, and 900 °C, resulting in the synthesis of Co nanocomposite catalysts, designated CoOx@NC-T, where T represents the pyrolysis temperature. XRD patterns revealed the formation of a mixture of Co phases, including metallic Co, CoO, and Co3O4, on the graphitic carbon. The variable pyrolysis temperature influenced the composition of the metallic Co phases. At 800 °C, the predominant phase is metallic Co, characterized by stronger and sharper diffraction peaks, while Co3O4 became the dominant at 900 °C. HR-TEM images demonstrated that core-shell structured Co nanoparticles, averaging 25 nm in size, were uniformly dispersed on the N-doped carbon matrix, in which Co and/or CoO as a core was covered by a shell of Co3O4 (Figure [7]). Correspondingly, the respective lattice spacings for Co, CoO, and Co3O4 were well resolved in the HRTEM image, aligning with Co 2p XPS. Raman spectra revealed the formation of graphitic carbon, characterized by the appearance of characteristic G and D band in each catalyst. BET analysis indicated that the catalyst CoOx@NC-T possess hierarchically micro-, meso-, and macro-pores with large specific surface area. Furthermore, the catalysts CoOx@NC-T exhibited high activity and excellent selectivity for the hydrogenation of nitrobenzene, with CoOx@NC-800 demonstrating significantly higher activity than the others.[44] A diverse set of nitroarenes, including those containing halo groups as readily reducible groups and amine, hydroxy, cyano, or ester, and amide groups, could be efficiently reduced to their corresponding amines with excellent selectivity, with all functional groups remaining untouched, indicating exclusive selectivity for nitro reduction (Scheme [7]). More importantly, the catalyst CoOx@NC-800 also displayed superior catalytic activity in a one-pot cascade reaction of the reductive amination of benzaldehyde and nitroarenes, yielding key imine intermediates.[59] A wide range of both aldehydes and nitroarenes reacted, with the nitroarene undergoing efficient reduction to the amine and then amination of the aldehyde to give the imines in high yields with tolerance of diverse functional groups (Scheme [8]).

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Figure 7 Schematic illustration of the preparation of CoOx@NC-T
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Scheme 7 Substrate scope for the hydrogenation of nitroarenes using the catalyst CoOx@NC-800
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Scheme 8 Substrate scope for the reductive coupling of nitroarenes with benzyl aldehydes using the catalyst CoOx@NC-800

The catalyst CoOx@NC-800 can be further utilized for the synthesis of pharmaceutically and biologically active benzimidazoles through direct one-pot coupling of phenylenediamines or ortho-amino-substituted nitrobenzenes with aldehydes.[60] In the case of ortho-amino nitrobenzenes as the coupling partner, the nitro group is first reduced to an amine, catalyzed by CoOx@NC-800 in the presence of H2 gas, followed by a sequential condensation-cyclization reaction. In contrast, the coupling of phenylenediamines with aldehydes can be conducted under mild, additive-free, and oxidant-free conditions, with water and H2 as the only byproducts (Scheme [9]). Additionally, CoOx@NC-800 is applicable to the chemoselective hydrogenation of α,β-unsaturated carbonyls and the one-pot cascade synthesis of saturated carbonyls via cross-aldol condensation of ketones with aldehydes in the presence of H2 (Scheme [10]).[61]

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Scheme 9 Substrate scope for the coupling reaction of aryl aldehydes and phenylenediamines using the catalyst CoOx@NC-800

Apart from its superior catalytic activity, CoOx@NC-800 demonstrated high stability and can be reused multiple times without a loss of activity or selectivity. Therefore, our study not only provides a new strategy for the preparation of hybrid multicomponent materials derived from biomass, but also highlights a novel, heterogeneous, active, and cost-effective catalyst for the expedient synthesis of pharmaceutically and biologically active compounds, including aniline derivatives, imines, benzimidazoles, and saturated carbonyls.

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Scheme 10 Substrate scope for the chemoselective hydrogenation of α,β-unsaturated carbonyls

To enhance the characteristics and catalytic performance of the cobalt nanocomposite supported on nitrogen-doped carbon derived from bamboo shoots, we implemented a heteroatom doping strategy by introducing electronegative phosphorus (P) atoms into the carbon support.[62] [63] A mixture of bamboo-shoot-derived biochar, Co(NO3)2, and PPh3 as the phosphorus source was pyrolyzed under a nitrogen atmosphere at 800 °C. The resulting catalyst was designated Co@NPC-800 (Figure [8a]). In contrast to Co@NC-800, the incorporation of P atoms resulted in the formation of a core-shell structure, wherein metallic Co nanoparticles served as the core, encapsulated by multiple layers of graphitic carbon. Characterization techniques, including XRD, TEM, and HR TEM, revealed that the core-shell structured Co nanoparticles, approximately 23 nm in diameter, were uniformly distributed on the nitrogen and phosphorus codoped carbon matrix. XPS analysis of N 1s, P 2p, and Co 2p spectra confirmed that N and P atoms were simultaneously incorporated into the carbon framework, resulting in the formation of C–N and P–C bonds, alongside Co-Nx and Co-P sites. These findings indicated a significant interaction between the Co nanoparticles and the N,P-codoped carbon layers.

The Co@NPC-800 catalyst demonstrated high catalytic activity for the transfer hydrogenation of functionalized nitroarenes using ammonium formate or formic acid as hydrogen donors (Figure [8b]).[62] A range of functionalized nitroarenes were efficiently and selectively reduced to their corresponding anilines with high yields and good compatibility with various functional groups. Mechanistic studies revealed that the synergy between N and P dopants in the graphitic carbon and the confined Co nanoparticles contributed to the high activity and exclusive selectivity. Furthermore, the Co@NPC-800 catalyst was effectively employed in one-pot selective N-formylation of nitroarenes to formamides, achieving good to high yields for a diverse array of nitroarenes (Figure [8b]).[63] Control experiments demonstrated that the N-formylation proceeded through a sequential reduction of the nitro group to an amine, followed by the formylation of the amine to N-formamide, with HCOOH or HCOONH serving as both reducing and formylating agents. Additionally, the Co@NPC-800 catalyst exhibited remarkable stability, allowing for convenient recycling up to six times without any loss of activity or changes to the core-shell nanostructures, underscoring its practicality.

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Figure 8 (a) Schematic illustration of the preparation of Co NPs coated with a N,P-codoped carbon shell and (b) switchable pathways of reductive transformation of nitroarenes catalyzed by Co@NPC-800

Introducing a second metal into the monometal-based nanocatalysts is an effective strategy to modulate their electronic and geometric properties, thereby improving catalytic activity, selectivity, and stability as well.[64] [65] Since the catalyst Co@NC-800 exhibited outstanding catalytic activity for the hydrogenation of nitroarenes and C=C bonds, consequently, we further tailored the surface by incorporating Pd single atom sites to extend its application to oxidation reactions.[66] The catalyst Co@NC-800 was dispersed into a ppm level aqueous solution of Pd, stirred for a specified duration, and subsequently dried under vacuum. The resultant solid was then pyrolyzed at 800 °C under a N2 atmosphere again, resulting in the formation of PdCo@NC-800 (Figure [9]). The XRD pattern showed no obvious difference for Co@NC-800 and PdCo@NC-800, indicating that Pd doping and the subsequent pyrolysis did not alter the crystallinity. No diffraction peaks corresponding to Pd species were observed in the PdCo@NC-800, suggesting a homogeneous dispersion. In contrast, Raman spectra showed that PdCo@NC-800 had a larger ID/IG ratio, suggesting that Pd doping resulted in increased defects in the catalyst. HR-TEM images confirmed the retention of the original structure of Co nanoparticles, which remained covered by Co3O4 upon Pd doping, consistent with the XRD result and indicating no significant influence on the morphology or size of Co nanoparticles after the incorporation of Pd. AC HAADF-STEM image revealed that Pd species were atomically dispersed on the catalyst surface. Co 2p XPS spectra showed that both Co@NC-800 and PdCo@NC-800 presented the same Co species, however, there was a 0.6 eV positive shift in the binding energies of the PdCo@NC-800 compared with Co@NC-800. This shift indicates an electronic interaction between Co nanoparticles and Pd species, attributed to charge transfer from Co to Pd due the higher electronegativity of Pd. In alignment with Co 2P XPS, the N 1s peak position of PdCo@NC-800 shifted to lower values relative to Co@NC-800, suggesting that Pd doping altered the electronic properties of the carbon support. Due to the trace amounts of the Pd loading, no Pd XPS signal could be observed. The FT k3-weighted XANES spectrum in the R space of the catalyst PdCo@NC-800 showed a weak peak at approximately 1.5 Å, corresponding to the first shell of the Pd-N/O path. No Pd-Pd paths at around 2.6 Å were observed. This confirms that Pd species are atomically dispersed within the catalyst Co@NC-800.

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Figure 9 Schematic illustration for preparation of the catalyst PdCo@NC-800

The catalyst PdCo@NC-800 exhibited high activity with excellent selectivity for the oxidation of sulfides to sulfoxide in CH2Cl2 with the presence of isobutyraldehyde under atmospheric pressure of O2 at room temperature.[66] An array of sulfides, including those containing potentially oxidizable functional groups and challenging linear alkyl sulfides, underwent efficient and selective oxidation to their respective sulfoxides in high yields (Scheme [11]). Furthermore, the catalyst PdCo@NC-800 demonstrated remarkable stability for successive reuse, maintaining both activity and structure. Experimental measurements and theoretical calculations reveal that the tailoring of single atom Pd leads to the formation of additional defects on the surface of cobalt nanocomposites and fosters a strong electronic interaction with Co nanoparticles. Their synergy promotes the adsorption and activation of O2 and isobutyraldehyde to generate reactive oxygen species, ultimately improving the reaction efficiency.

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Scheme 11 Substrate scope for the oxidation of sulfides to sulfoxides using the catalyst PdCo@NC-800

# 4

Ni-Based Catalysts

We further extended our preparation strategy to the synthesis of Ni-based-nanostructured catalysts. By pyrolyzing a mixture of bamboo-shoot-derived biochar and Ni source (Ni(OAc)2) under a N2 atmosphere across varying pyrolysis temperatures, referred to as Ni@NC-T, where T represents the temperature (T = 700, 800, and 900 °C), we successfully synthesized a spatially confined Ni nanocatalyst.[67] The pyrolysis temperature significantly influenced the morphology and structure of the catalysts. TEM images reveal that Ni@NC-T exhibited a consistent morphology, displaying a uniform dispersion of particles on graphitic carbon. The particle sizes gradually increased from 18.2 to 21.8 nm with an increase of pyrolysis temperature. In sharp contrast, HRTEM images indicated substantial structural differences among the catalysts. For Ni@NC-700, the metallic Ni nanoparticles with uniform size were distributed on the graphitic carbon. However, for the catalyst Ni@NC-800 and Ni@NC-900, a core-shell structure, with Ni nanoparticles as the core and a carbon layer as the shell, homogeneously dispersed on the graphitic carbon. Notably, the thickness of carbon layers in the catalyst Ni@NC-900 was considerably larger than in Ni@NC-800, indicating that high temperatures promote the formation of multiple carbon layers to encapsulate Ni nanoparticles (Figure [10]).

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Figure 10 Schematic illustration of the preparation of the catalysts Ni@NC-T
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Figure 11 Illustration of the preparation of the catalyst Ni2P@NPC-T
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Scheme 12 Illustration of the synthesis of quinazolines, quinazolinones, and imidazoles using the catalyst Ni2P@NPC-800

XRD patterns further confirmed the formation of metallic Ni nanoparticles phase. BET analysis showed that they posses large surface area and hierarchical pores. N 1s XPS spectra confirmed the doping of N atoms into the carbon framework, resulting in the formation of pyridinic, pyrrolic, graphitic, and oxidized N species. Ni 2p XPS spectra indicated that the binding energies for Ni@NC-800 and Ni@NC-900 negatively shifted compared to Ni@NC-700, implying an interfacial electron transfer from N-doped carbon layers to the Ni nanoparticles. The core-shell structure effectively protects Ni nanoparticles from aggregation to substantially boost the stability, while also introducing steric and electronic effects that influence the surface of the Ni nanoparticles via an intimate interfacial interaction with N-doped carbon layers. Consequently, the resulting catalyst exhibited both high activity and selectivity for semihydrogenation of alkynes to alkenes. A broad set of terminal and internal alkynes were efficiently reduced to their respective alkenes in a highly selective manner. Under identical conditions, the catalyst Ni@NC-700, which lacked a carbon layer, showed relatively high reaction efficiency, however, overhydrogenation of alkenes to undesired alkanes became significant with prolonged reaction times. Control experiments demonstrated that the sterically core-shell structure inhibited H2 activation and desorption but thermodynamically facilitated the desorption of alkenes from the surface, thus rationalizing the enhanced selectivity to alkenes. In addition, the catalyst Ni@NC-800 could be recovered and recycled up to 8 times with a negligible loss in activity and selectivity, maintaining its unique core-shell structure without no aggregation of Ni nanoparticles or leaching.

Heteroatom-doping strategy was also employed to synthesize Ni-based-nanostructured catalysts. In this context, phytic acid was utilized as P source. We synthesized ultrafine Ni2P nanoparticles supported on N,P-codoped porous carbon, denoted as Ni2P@NPC-800, through the pyrolysis of a mixture of bamboo-shoot-derived biochar, Ni(OAc)2, and phytic acid under a constant nitrogen flow at 800 °C (Figure [11]).[68] [69] TEM images confirmed that the ultrafine Ni2P nanoparticles had a narrow size distribution (3.2 ± 0.7 nm) and were uniformly dispersed on the graphite carbon. HR-TEM image presented well-resolved lattice fringe spacing corresponding to Ni2P phase, further corroborated by XRD patterns. N 1s and P 2p XPS spectra confirmed that N and P atoms were co-doped into the carbon framework, resulting in the formation of pyridinic, pyrrolic, graphitic, and oxidized N species, along with Ni–P and P–C bonds. The catalyst Ni2P@NPC-800 demonstrated high activity and stability for the synthesis of pharmaceutically important N-heterocycles, including quinazolines, quinazolinones, and imidazoles, through oxidative cross-coupling of a wide range of alcohols with diamines or 2-aminobenzamides using atmospheric air as the sole oxidant under mild reaction conditions (Scheme [12]).[68] Furthermore, the catalyst Ni2P@NPC-800 could be applied to the synthesis of alkynyl thioethers via the cross-dehydrogenative coupling of alkynes and thiols under base- and ligand-free conditions.[69] A broad range of alkynes and thiols could be efficiently coupled to give the corresponding alkynyl thioethers, yielding good to high yields while tolerating various functional groups (Scheme [13]). Control experiments indicated that pyridinic N atoms facilitated the activation of terminal alkynes via hydrogen bonding interactions, playing a crucial role in the reaction.


# 5

Cu-Based Catalysts

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Scheme 13 Highly dispersed Ni2P nanoparticles on N,P-codoped carbon for efficient cross dehydrogenative coupling to access alkynyl thioethers

In the preparation of carbon-based non-precious metal nanocatalysts derived from bamboo shoots, our earlier studies indicated that all synthesized catalysts exhibit structural and compositional heterogeneity. This heterogeneity complicates the identification of catalytically active sites and the correlation of the activity-structure function. We subsequently aimed to synthesize a single atom catalyst characterized by atomic dispersion, high metal atom utilization, and a well-defined local structure. Fortunately, we successfully synthesized a Cu single atom catalyst from bamboo shoots. Pyrolysis of a mixture of bamboo-shoot-derived biochar and Cu(NO3)2 under an N2 atmosphere at 800 °C yielded the Cu single atom catalyst, designated Cu1/NC-800 (Figure [12]).[47] [70] The key to achieving Cu single atom sites was the reduction of Cu loadings. The loading content of Cu in the catalyst Cu1/NC-800 was measured to be 1.28 wt% by ICP-AES. Comprehensive characterizations, including XRD, BET, XPS, HRTEM, EELS, and XAFS, confirm that Cu atoms are atomically dispersed on the N-doped porous carbon. The EXAFS fitting results indicate a coordination number of approximately 2.2 for Cu-N, indicating that the isolated Cu atoms are coordinated by two N atoms to form Cu-N2 local configuration. This represents the first report of the direct synthesis of a single atom catalyst without the post-treatment processes commonly employed in previous state-of-the-art strategies, significantly alleviating preparation cost and waste emissions. The catalyst Cu1/NC-800 exhibited a superior catalytic activity, selectivity, and stability for efficient Glaser–Hay coupling of a broad spectrum of terminal alkynes to access various symmetrical and unsymmetrical 1,3-diynes using atmospheric air as the oxidant under base- and ligand-free conditions (Scheme [14]).[47] The catalytic activity of the Cu1/NC-800 surpasses the previously reported heterogeneous and even homogeneous Cu-based catalysts.

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Scheme 14 Schematic illustration of Glaser–Hay coupling using the catalyst Cu1/NC-800
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Figure 12 Schematic illustration of the synthesis of Cu1/NC-800

Moreover, the catalyst Cu1/NC-800 is applicable to the azide-alkyne cycloaddition reaction (AAC) at room temperature. A broad set of 1,4-disubstituted 1,2,3-triazoles were synthesized in high to excellent yields with good tolerance of various functional groups (Scheme [15]).[70]

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Scheme 15 Schematic illustration of azide-alkyne cycloaddition (AAC) using the catalyst Cu1/NC-800

# 6

Conclusion

In this personal account, our recent progress in the design, synthesis, and applications of biomass-derived carbon-based non-precious metal nanocatalysts is summarized. Our research reveals that the morphology and structure of these nanocatalysts can be effectively adjusted by varying pyrolysis conditions and by introducing second element. A set of nanostructured catalysts that exhibit homogeneous dispersion of nanoparticles or nanocomposites, core-shell structures, coexistence of nanoparticles/nanoclusters with single atom sites, and single atom sites were synthesized. These catalysts demonstrate outstanding catalytic performance and selectivity for various organic transformation while maintaining strong stability. This advancement provides an effective solution to the challenges of low activity and selectivity, and poor stability. We hope this account offers new insights into the development of non-precious metal catalysts.


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Conflict of Interest

The authors declare no conflict of interest.

Acknowledgment

The author acknowledges the following co-workers and collaborators. The research group co-workers: Miss Guijie Ji, Miss Yanan Duan, Dr. Xiaoxu Dong, Dr. Tao Song, Dr. Peng Ren, Dr. Zhiming Ma, Dr. Xiaoxue Wang, and Mr. Zhaozhan Wang. Our collaborators: Prof. Dr. Xiufang Chen (Zhejiang Sci-Tech University), Prof. Dr. Jianliang Xiao (Liverpool University), Prof. Dr. Youzhu Yuan (Xiamen University), Prof. Dr. Ken Motokura (Yokohama National University), and Prof. Dr. Zhemin Shen (Shanghai Jiaotong University).


Corresponding Author

Yong Yang
Key Laboratory of Photoelectric Conversion and Utilization of Solar Energy, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences
Qingdao 266101
P. R. of China   

Publication History

Received: 20 January 2025

Accepted: 07 February 2025

Article published online:
26 March 2025

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Figure 1 Schematic illustration of the preparation of a series of carbon-based non-precious metal nanocatalysts
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Figure 2 (A) TEM and (B and C) HR-TEM images of the catalyst Fe-Fe3C@NC-800, the inset shows the size distribution of metallic Fe nanoparticles; (D) HAADF-STEM and the corresponding EDX elemental mappings of individual Fe-Fe3C@NC-800; (E) schematic illustration of the catalyst Fe-Fe3C@NC-800; and (F) XRD pattern of the catalyst Fe-Fe3C@NC-800
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Scheme 1 Substrate scope for the synthesis of quinazolines and quinazolinones using the catalyst Fe-Fe3C@NC-800
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Figure 3 Illustration of the removal of NPs and NCs via an acid etching
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Scheme 2 Substrate scope of the oxidative coupling reaction of primary amines using the catalyst Fe-NC-SA
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Figure 4 Schematic illustration of the bifunctional catalyst Fe@NPC-800
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Scheme 3 Substrate scope of alkenes for the synthesis of ketones using the catalyst Fe@NPC-800
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Scheme 4 Substrate scope of internal alkenes for the synthesis of α-diketones using the catalyst Fe@NPC-800
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Scheme 5 Substrate scope of terminal alkenes for the synthesis of α-keto acids using the catalyst Fe@NPC-800
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Scheme 6 Schematic illustration of the one-pot cascade synthesis of α-diketones from aldehydes and ketones
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Figure 5 Schematic illustration of the single-phase pyrite FeS2/NSC
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Figure 6 Illustration of hydrogenation of functionalized nitrobenzenes
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Figure 7 Schematic illustration of the preparation of CoOx@NC-T
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Scheme 7 Substrate scope for the hydrogenation of nitroarenes using the catalyst CoOx@NC-800
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Scheme 8 Substrate scope for the reductive coupling of nitroarenes with benzyl aldehydes using the catalyst CoOx@NC-800
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Scheme 9 Substrate scope for the coupling reaction of aryl aldehydes and phenylenediamines using the catalyst CoOx@NC-800
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Scheme 10 Substrate scope for the chemoselective hydrogenation of α,β-unsaturated carbonyls
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Figure 8 (a) Schematic illustration of the preparation of Co NPs coated with a N,P-codoped carbon shell and (b) switchable pathways of reductive transformation of nitroarenes catalyzed by Co@NPC-800
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Figure 9 Schematic illustration for preparation of the catalyst PdCo@NC-800
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Scheme 11 Substrate scope for the oxidation of sulfides to sulfoxides using the catalyst PdCo@NC-800
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Figure 10 Schematic illustration of the preparation of the catalysts Ni@NC-T
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Figure 11 Illustration of the preparation of the catalyst Ni2P@NPC-T
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Scheme 12 Illustration of the synthesis of quinazolines, quinazolinones, and imidazoles using the catalyst Ni2P@NPC-800
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Scheme 13 Highly dispersed Ni2P nanoparticles on N,P-codoped carbon for efficient cross dehydrogenative coupling to access alkynyl thioethers
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Scheme 14 Schematic illustration of Glaser–Hay coupling using the catalyst Cu1/NC-800
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Figure 12 Schematic illustration of the synthesis of Cu1/NC-800
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Scheme 15 Schematic illustration of azide-alkyne cycloaddition (AAC) using the catalyst Cu1/NC-800