Abstract
Direct propylene epoxidation using Au-based catalysts is an important gas-phase reaction and is clearly a promising route for the future industrial production of propylene oxide (PO). For instance, gold nanoparticles or clusters that consist of a small number of atoms demonstrate unique and even unexpected properties, since the high ratio of surface to bulk atoms can provide new reaction pathways with lower activation barriers. Support materials can have a remarkable effect on Au nanoparticles or clusters due to charge transfer. Moreover, Au (or Au-based alloy, such as Au–Pd) can be loaded on supports to form active interfacial sites (or multiple interfaces). Model studies are needed to help probe the underlying mechanistic aspects and identify key factors controlling the activity and selectivity. The current theoretical/computational progress on this system is reviewed with respect to the molecular- and catalyst-level aspects (e.g., first-principles calculations and kinetic modeling) of propylene epoxidation over Au-based catalysts. This includes an analysis of H2 and O2 adsorption, H2O2 (OOH) species formation, epoxidation of propylene into PO, as well as possible byproduct formation. These studies have provided a better understanding of the nature of the active centers and the dominant reaction mechanisms, and thus, could potentially be used to design novel catalysts with improved efficiency.
Highlights
Due to the growing environmental issues in chemical synthesis and processing, there has been increasing interest in the development of new processes for minimizing pollution and reducing energy consumption
We focus on the selective epoxidation of propylene to yield propylene oxide (PO) using heterogeneous gold-based catalysts
The catalytic activity of gold and gold alloy nanoparticles has been ascribed to various mechanisms, involving reactions occurring at neutral gold atoms that differ from bulk gold atoms, quantum size effects that change the electronic structures of nanoparticles, or charge modification of gold atoms through the interaction with oxide supports [6,7,8]
Summary
Due to the growing environmental issues in chemical synthesis and processing, there has been increasing interest in the development of new processes for minimizing pollution and reducing energy consumption. We focus on the selective epoxidation of propylene to yield propylene oxide (PO) using heterogeneous gold-based catalysts. Computational studies have been enormously valuable in describing the structural and electronic character of size-selected gold nanoparticles and determining the catalytic reaction mechanisms for the propylene epoxidation process, and have already yielded important outcomes for the development of catalytic materials. Motivated by these growing computational investigations and the need to incorporate this theoretical knowledge into catalyst design, we review the theoretical studies relevant to direct propylene epoxidation in the gas phase with Au-based catalysts. Conclusions and perspectives are given, along with current challenges and opportunities in the field
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