Silver/graphene nanocomposites as catalysts for the reduction of p -nitrophenol to p -aminophenol: Materials preparation and reaction kinetics studies

Advances in Graphene/Inorganic Nanoparticle Composites for Catalytic Applications

Graphene-based nanocomposites with inorganic (metal and metal oxide) nanoparticles leads to materials with high catalytic activity for a variety of chemical transformations. Graphene and its derivatives such as graphene oxide, highly reduced graphene oxide, or nitrogen-doped graphene are excellent support materials due to their high surface area, their extended π-system, and variable functionalities for effective chemical interactions to fabricate nanocomposites. The ability to fine-tune the surface composition for desired functionalities enhances the versatility of graphene-based nanocomposites in catalysis. This review summarizes the preparation of graphene/inorganic NPs based nanocomposites and their use in catalytic applications. We discuss the large-scale synthesis of graphene-based nanomaterials. We have also highlighted the interfacial electronic communication between graphene/inorganic nanoparticles and other factors resulting in increased catalytic efficiencies.

Pumpkin-derived N-doped porous carbon for enhanced liquid-phase reduction of 2-methyl-4-nitrophenol

Metal-free catalysts with environmental friendless, cost-competitiveness and less susceptibility to leaching and poisoning over metal-based catalysts, have revolutionized in the catalysis domain. In this respect, we herein report the first application of cheap and abundant pumpkin-derived N-doped porous carbon for the reduction of 2-methyl-4-nitrophenol assisted by NaBH₄. The obtained catalyst is cost-competitive, efficient and robust, with an attractive mass-normalized rate constant of 4.73 s^-1 g^-1 and good recycling performance. Systematical analyses demonstrate that the 2-methyl-4-nitrophenol reduction reaction catalyzed by the N-doped carbon proceeds through the Langmuir-Hinshelwood kinetics and the performance enhancement benefits from the strong adsorption and activation of the substrates induced by the electronic modulation in the carbon framework via N-doping. This study opens up new avenues for the high-value use of pumpkin as well as the development of metal-free strategy in more catalytic applications.

Highly selective oxidation of styrene to benzaldehyde over a tailor-made cobalt oxide encapsulated zeolite catalyst

A tailor-made catalyst with cobalt oxide particles encapsulated into ZSM-5 zeolites (Co₃O₄@HZSM-5) was prepared via a hydrothermal method with the conventional impregnated Co₃O₄/SiO₂ catalyst as the precursor and Si source. Various characterization results show that the Co₃O₄@HZSM-5 catalyst has well-organized structure with Co₃O₄ particles compatibly encapsulated in the zeolite crystals. The Co₃O₄@HZSM-5 catalyst was employed as an efficient catalyst for the selective oxidation of styrene to benzaldehyde with hydrogen peroxide as a green and economic oxidant. The effect of various reaction conditions including reaction time, reaction temperature, different kinds of solvents, styrene/H₂O₂ molar ratio and catalyst dosage on the catalytic performance were systematically investigated. Under the optimized reaction condition, the yield of benzaldehyde can achieve 78.9% with 96.8% styrene conversion and 81.5% benzaldehyde selectivity. Such an excellent catalytic performance can be attributed to the synergistic effect between the confined reaction environment and the proper acidic property. In addition, the reaction mechanism with Co₃O₄@HZSM-5 as the catalyst for the selective oxidation of styrene to benzaldehyde was reasonably proposed.

Metallic cobalt nanoparticles imbedded into ordered mesoporous carbon: A non-precious metal catalyst with excellent hydrogenation performance

Ordered mesoporous carbon (OMC)-metal composites have attracted great attention owing to their combination of high surface area, controlled pore size distribution and physicochemical properties of metals. Herein, we report the cobalt nanoparticles/ordered mesoporous carbon (CoNPs@OMC) composite prepared by a one-step carbonization/reduction process assisted by a hydrothermal pre-reaction. The CoNPs@OMC composite presents a high specific surface area of 544m²g^-1, and the CoNPs are uniformly imbedded or confined in the ordered mesoporous carbon matrix. When used as a non-precious metal-containing catalyst for hydrogenation reduction of p-nitrophenol and nitrobenzene, it demonstrates high efficiency and good cycling stability. Furthermore, the CoNPs@OMC composite can be directly used to catalyze the Fischer-Tropsch synthesis for the high-pressure CO hydrogenation, and presents a good catalytic selectivity for C₅⁺ hydrocarbons. The excellent catalytic performance of the CoNPs@OMC composite can be ascribed to synergistic effect between the high specific surface area, mesoporous structure and well-imbedded CoNPs in the carbon matrix.