In heterogenous catalysis, many famous theories have been developed to study the interactions between catalyst surface and reactant molecules, for example, L-H and E-R mechanisms. One aspect that is often overlooked when we emphasize on the study of surface chemistry is the adsorption-compression (A-C) effect, which suggests the compression potential energy between the adsorbed reactants can also play a big part. However, few experimental work can provide promising support. Herein, we studied the effect of A-C based on one of the most environmentally concerned reactions: direct NO decomposition (deNO). For direct deNO over Cu-ZSM-5, the commonly believed rate-limiting step occurs when two proximal NO molecules absorbed on neighboring Cu active sites react to form N-N bond and produce intermediate N<sub>2</sub>O, during which the compression between two absorbed NO molecules can generate a potential energy, which gives a potential boost for the reactant to overcome energy barrier. Therefore, we can hypothesize that CuZSM-5 with smaller distances between two neighboring Cu sites should have higher activity of NO decomposition. As seen in Table 1, both the reaction rates and compression energies increase with the decrement of Si/Al ratios. By referring distances of CuZSM-5 samples in other works, which has very similar Si/Al and Cu/Al with our CuZSM-5 samples, we found Cu-Cu distances decrease with the decrement of Si/Al ratios, and the compression energies increase with Cu-Cu distances decrease (Figure 1). Therefore, we can conclude that the compression energy could facilitate NO decomposition on CuZSM-5, and CuZSM-5 with smaller Cu-Cu distances, which lead to higher compression energy has higher activity of NO decomposition. Such observation also could propose a new direction of tailoring the new catalysts with optimal distances of active sites.

Application of adsorption-compression theory in gas phase heterogeneous catalytic reaction: Promising proof through direct NO decomposition over Cu-ZSM-5

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.