Understanding the Enhanced Catalytic Performance of Ultrafine Transition Metal Nanoparticles–Graphene Composites

Abstract

Catalysis, as the key to minimize the energy requirement and environmental impact of today's chemical industry, plays a vital role in many fields directly related to our daily life and economy, including energy generation, environment control, manufacture of chemicals, medicine synthesis and etc. Rational design and fabrication of highly efficient catalysts have become the ultimate goal of today's catalysis research. For the purpose of handling and product separation, heterogeneous catalysts are highly preferred for industrial applications and a large part of which are the composites of transition metal nanoparticles (TM NPs). With the fast development of nano-science and nano-technology and assisted with theoretical investigations, basic understanding on tailoring the electronic structure of these nano-composites has been gained, mainly by precise control of the composition, morphology, interfacial structure and electronic states. With the rise of graphene, chemical routes to prepare graphene were developed and various graphene based composites were fabricated. Transition metal nanoparticle-reduced graphene oxide (TM-rGO) composites have attracted considerable attention, because of their intriguing catalytic performance which have been extensively explored for energy-and environment-related applications to date. This review summarizes our recent experimental and theoretical efforts on understanding the superior catalytic performance of subnanosized TM NPs -rGO composites. 3Tailoring catalysts and catalytic processes have long been the 'Holy Grail' of catalytic chemistry. The key elementary steps of catalytic reactions, such as the adsorption of reactants, the diffusion of intermediates and the desorption of products, all involve bond formation and dissociation and are associated with electron transfer among the catalyst and the adsorbed reaction species. According to the frontier molecular orbital theory, the strength of the bonding of reactants onto catalyst surfaces is closely related to the symmetry and occupation of the orbitals of reactants, and is strongly correlated with the difference in the energy levels of the reactants and those of the catalyst. Norskov and coworkers extended this idea to periodic transition metal systems and introduced the d-band center theory based on a large body of experimental and theoretical results, which emphasizes that the density of TM-d states around the Fermi level is an important factor affecting catalytic reactions.1 To this end, controlled modulation of the spatial and energy distribution of the catalyst states would be a feasible way to lower the energy barriers and facilitate the adsorption and subsequent bonding evolution between reactants over the catalyst on the specific reaction paths to achieve high reactivity and so as the product selectivity.The conventional methods to influence and adjust the electronic structure of a catalyst are to develop interactions and charge transfer among the primary catalytic composition with various additives. Alloying and d...

The formation and evolution of carbonate species in CO oxidation over mono-dispersed Fe on graphene

“…The dominant role of the electronic structure in the performance of a specific catalyst has been well recognized. 34,45,46 Considering the monodispersed under-coordinated nature of metals in SACs and the dynamic adsorption and conversion of substrates in reaction conditions, the impact of reaction species on metal centers would be more pronounced, and it may stabilize or even drive further evolution of metal centers, switch the reaction mechanisms and contribute to the conversion and product selectivity. [47][48][49][50][51] To this end, mechanism investigations on SAC-catalyzed chemical conversion in conditions relevant to experiments would be more helpful to rationalize the understanding of the observed superior performance of SACs.…”

Major Advances and Challenges in Heterogeneous Catalysis for Environmental Applications: A Review

“…For example, graphene (or its unexfoliated form [31]) based materials were found to be a great supporting material for this purpose [29,[32][33][34][35][36][37]. This has enabled various environmentally-friendly and useful applications in electrochemical energy storage/conversion and heterogeneous catalysis.…”