Hydrogenation of Furfural with Nickel Nanoparticles Stabilized on Nitrogen-Rich Carbon Core-Shell and Its Transformations for the Synthesis of γ-Valerolactone in Aqueous Conditions

Highly Efficient and Selective Hydrogenation of Biomass-Derived Furfural Using Interface-Active Rice Husk-Based Porous Carbon-Supported NiCu Alloy Catalysts

A series of bimetallic NixCuy catalysts with different metal molar ratios, supported on nitric acid modified rice husk-based porous carbon (RHPC), were prepared using a simple impregnation method for the liquid-phase hydrogenation of furfural (FFA) to tetrahydrofurfuryl alcohol (THFA). The Ni2Cu1/RHPC catalyst, with an average metal particle size of 9.3 nm, exhibits excellent catalytic performance for the selective hydrogenation of FFA to THFA. The 100% conversion of FFA and the 99% selectivity to THFA were obtained under mild reaction conditions (50 °C, 1 MPa, 1 h), using water as a green reaction solvent. The synergistic effect of NiCu alloy ensures the high catalytic activity. The acid sites and oxygen-containing functional groups on the surface of the modified RHPC can enhance the selectivity of THFA. The Ni2Cu1/RHPC catalyst offers good cyclability and regenerability. The current work proposes a simple method for preparing an NiCu bimetallic catalyst. The catalyst exhibits excellent performance in the catalytic hydrogenation of furfural to tetrahydrofurfuryl alcohol, which broadens the application of non-noble metal bimetallic nanocatalysts in the catalytic hydrogenation of furfural.

Graphene-like wrapped Ni@C catalyst with magnetic recyclability for selective hydrogenation of nitro-aromatics

The graphene-like wrapped Ni@C catalysts were facilely synthesized by a modified sol-gel method. Nickel nitrate and citric acid (CA) were adopted as the raw materials to form sol-gel mixture. Under the circumstances, the additive CA were employed not only as a complexing agent but also as a carbon source. It is found that the calcination temperature and the mole ratios between Ni and CA are the key factors affecting the physical property and the catalytic performance of catalysts in the conversion of nitroarenes into corresponding anilines. The results show that the Ni@C-500(1:1) catalyst exhibited the best performance in the hydrogenation ofo-chloronitrobenzenes (o-CNB) too-chloroanilines (o-CAN). The yield ofo-CAN was achieved at 100% wheno-CNB was completely converted at 40.0 °C under 2.0 MPa H₂for 2.0 h. Furthermore, the Ni@C-500(1:1) catalyst could be separated and recovered easily after reaction by an external magnetic field. The investigated results indicate that the Ni@C-500(1:1) catalyst remained higher activity after using twelve times. More importantly, this kind of catalyst is also active for the selective hydrogenation of other nitroarenes into the corresponding anilines. This new synthetic method may pave a way for producing low-cost Ni@C catalysts on a large scale, which is attractive for industrial anilines applications.

Advanced Carbon-Based Nanocatalysts and their Application in Catalytic Conversion of Renewable Platform Molecules

The transformation of renewable platform molecules to produce value-added fuels and fine-chemicals is a promising strategy to sustainably meet future demands. Owing to their finely modified electronic and geometric properties, carbon-based nanocatalysts have shown great capability to regulate their catalytic activity and stability. Their well-defined and uniform structures also provide both the opportunity to explore intrinsic reaction mechanisms and the site-requirement for valorization of renewable platform molecules to advanced fuels and chemicals. This Review highlights the progress achieved in carbon-based nanocatalysts, mainly by using effective regulation approaches such as heteroatom anchoring, bimetallic synergistic effects, and carbon encapsulation to enhance catalyst performance and stability, and their applications in renewable platform molecule transformations. The foundation for understanding the structure-performance relationship of carbon-based catalysts has been established by investigating the effect of these regulation methods on catalyst performance. Finally, the opportunities, challenges and potential applications of carbon-based nanocatalysts are discussed.

Mechanism of Catalytic Transfer Hydrogenation for Furfural Using Single Ni Atom Catalysts Anchored to Nitrogen-Doped Graphene Sheets

Catalytic transfer hydrogenation (CTH) of α,β-unsaturated aldehydes using single metal atom catalysts supported on nitrogen-incorporated graphene sheet (M-N_x-Gr) materials has attracted increasing attention recently, yet the reaction mechanism remains to be explored. Compared to the Ni-N₄-Gr model in which the dissociation of isopropanol is highly unfavorable as a result of steric hindrance and inertness of the Ni-N₄ site embedded in graphene, the Ni-N₃ site in Ni-N₃-Gr is more active and facilitates the formation of *H with isopropanol as the H donor, where the dissociation of H from isopropanol with an energy barrier of 0.83 eV is the rate-determining step. An alternative reaction path starts from the coadsorption of isopropanol and furfural molecules at the Ni-N₃ site, followed by a direct hydrogen transfer between the two molecules; however, the rate-determining step has a much higher energy barrier of 1.32 eV. Our calculations suggest that the hydrogenation of the aldehyde group is kinetically more favorable than the C═C hydrogenation, revealing the high chemoselectivity of furfural to furfuryl alcohol. Our investigations reveal that the CTH mechanism using the Ni-N₃-Gr catalyst is different from that on traditional metal oxides, where the former has only one single active site, while two active sites are required for the latter. The proposed reaction mechanism of CTH for furfural in this study should be helpful to guide the design of single metal atom catalysts with appropriate N coordination for application in chemoselective hydrogenation reactions.

MoOx-Decorated Co-Based Catalysts toward the Hydrodeoxygenation Reaction of Biomass-Derived Platform Molecules

Catalytic conversion of a biomass derivative (levulinic acid, LA) to a high value-added product (γ-valerolactone, GVL) has attracted much attention, in which the control of catalytic selectivity plays an important role. Herein, a stepwise method was developed to prepare Co-MoO_x catalysts via topological transformation (calcination reduction) from layered double hydroxide (Mo/CoAl-LDH) precursors. X-ray diffraction, high-resolution transmission electron microscopy, and hydrogen temperature-programmed reduction demonstrate the formation of MoO_x-decorated Co structures of Co-MoO_x samples. Remarkably, the sample that is reduced at 500 °C is featured with the most abundant interfacial Co^δ+ (denoted as Co-MoO_x-500), which exhibits an excellent catalytic performance toward the hydrodeoxygenation (HDO) reaction of several biomass-derived platform molecules (furfural, FAL; succinic acid, SA; 5-hydroxymethyl-furfural, HMF; and levulinic acid, LA). Especially, this optimal catalyst displays a high yield (99%) toward the HDO reaction of LA to GVL, which stands at the highest level among non-noble metal catalysts. The combination of in situ FT-IR characterization and theoretical calculation further confirms that interfacial Co^δ+ sites in Co-MoO_x-500 act as adsorption active sites for the polarization of a C═O bond in an LA molecule, which simultaneously promotes C═O hydrogenation and C-O cleavage. Moreover, the MoO_x overlayer suppresses the formation of byproducts by covering the Co⁰ sites. This work offers a cost-effective and efficient catalyst, which can be potentially applied in catalytic conversion of biomass-derived platform molecules.

Engineering of Yolk/Core-Shell Structured Nanoreactors for Thermal Hydrogenations

Heterogeneous hydrogenation reactions are of great importance for chemical upgrading and synthesis, but still face the challenges of controlling selectivity and long-term stability. To improve the catalytic performance, many hydrogenation reactions utilize special yolk/core-shell nanoreactors (YCSNs) with unique architectures and advantageous properties. This work presents the developmental and technological challenges in the preparation of YCSNs that are potentially useful for hydrogenation reactions, and provides a summary of the properties of these materials. The work also addresses the scientific challenges in applications of these YCSNs in various gas and liquid-phase hydrogenation reactions. The catalyst structures, catalytic performance, structure-performance relationships, reaction mechanisms, and unsolved problems are discussed too. Also, a brief outlook and opportunities for future research in this field are presented. This work on the advancements in YCSNs might inspire the creation of new materials with desired structures for achieving maximal hydrogenation performances.

Selective Hydrogenation of Furfural over the Co-Based Catalyst: A Subtle Synergy with Ni and Zn Dopants

A multimetal doping strategy has aroused extensive attention in promoting a non-noble catalyst for selective hydrogenation reaction. Herein, a multimetallic catalyst (NiCoZn@CN) with excellent catalytic performance for hydrogenation of furfural (FAL) to furfuryl alcohol (FOL) is prepared through a facile, inexpensive, and efficient pyrolysis method. Using H₂ as a H donor, extremely high selectivity (>99%) with 100% conversion is attained over the optimal NiCoZn@CN-600 catalyst. The subtle synergy between Co and Ni, Zn dopants, which remarkably promotes the performance of the Co-based catalyst, is revealed. In the NiCoZn@CN system, Co⁰ is proven to be the main active site, whose content is greatly improved by Ni and Co dopants. Additionally, the Ni dopant could also benefit activation of H₂ and the Zn dopant could enhance metal nanoparticle dispersion and the porous structure of the catalyst. In situ FTIR indicates that the vertical adsorption mode of FAL with the O_aldehyde terminal on NiCoZn@CN-600 ensures a selective hydrogenation process. With a N-doped carbon matrix, NiCoZn@CN-600 shows good cycling stability in five times run. NiCoZn@CN-600 is also competent in the catalytic transfer hydrogenation (CTH) of FOL, affording >99% yield with 2-propanol as a H donor. This study opens an avenue toward rational design of multimetallic doping catalysts with high selectivity for challenging reactions in the conversion of biomass-derived compounds.

Falling Leaves Return to Their Roots: A Review on the Preparation of γ-Valerolactone from Lignocellulose and Its Application in the Conversion of Lignocellulose

γ-Valerolactone (GVL), derived from renewable lignocellulosic biomass, has been considered as a cost-competitive and green platform chemical. With the increasingly prominent environmental problems, a deep understanding of the preparation and transformation of GVL is highly needed. Based on the latest progress made with GVL, preparation and applications of GVL are summarized and discussed in this Review. In particular, the state-of-the-art in catalytic production of GVL is described based on the use of noble-metal and non-noble-metal catalysts. The application of GVL for the valorization of lignocellulose would improve the yield of target products such as sugar monomers and furfural. Thus, GVL can be produced from lignocellulose and simultaneously it can also be used for the valorization of lignocellulose, just as in the sustainable and renewable cycle, "the falling leaves returns to their roots". This Review is expected to provide valuable reference and new proposal for the further development and better utilization of GVL.

Hydrogenation of Furfural to Cyclopentanone under Mild Conditions by a Structure-Optimized Ni-NiO/TiO2 Heterojunction Catalyst

The catalytic conversion of biomass-derived furfural (FFA) into cyclopentanone (CPO) in aqueous solution is an important pathway to obtain sustainable resources. However, the conversion and selectivity under mild conditions are still unsatisfactory. In this study, a catalyst consisting of Ni-NiO heterojunction supported on TiO₂ with optimized composition of anatase and rutile (Ni-NiO/TiO₂ -Re450) is prepared by pyrolysis at 450 °C. With Ni-NiO/TiO₂ -Re450, as catalyst, complete conversion of FFA and 87.4 % yield of CPO are achieved under mild reaction conditions (1 MPa, 140 °C, 6 h). 95.4 % FFA conversion is retained up to the fifth run, indicating the high stability of the catalyst. Multiple characterizations, control experiments, and theoretical calculations demonstrate that the good catalytic performance of Ni-NiO/TiO₂ -Re450 can be attributed to a synergistic effect of the Ni-NiO heterojunction and the TiO₂ support. This low-cost catalyst may expedite the catalytic upgrading and practical application of biomass-derived chemicals.

MOF-derived uniform Ni nanoparticles encapsulated in carbon nanotubes grafted on rGO nanosheets as bifunctional materials for lithium-ion batteries and hydrogen evolution reaction

The rational-design and synthesis of transition-metal compounds with outstanding electrochemical activity and durability for renewable energy systems have attracted tremendous research interest in recent years. Herein, we report a facile and unique strategy to synthesize N-doped carbon nanotube-encapsulated Ni nanoparticles on reduced graphene oxide (Ni@NC-rGO). The optimized nanostructure determines the synergetic effects among the Ni nanoparticles, N-doped CNTs and graphene nanosheets, thus resulting in extraordinary electrochemical performances. When applied as an anode for lithium-ion batteries (LIBs), the Ni@NC-rGO electrode displayed high reversible capacity, stable cycling performance and superior rate capability. Moreover, the resulting Ni@NC-rGO nanocomposites exhibited low overpotential and considerable durability for the hydrogen evolution reaction (HER). Our study may provide a feasible methodology for the preparation of high-performance nanostructured materials for practical energy storage and conversion applications.