Wentao Xu

A new type of power energy for accelerating chemical reactions: the nature of a microwave-driving force for accelerating chemical reactions

The use of microwave (MW) irradiation to increase the rate of chemical reactions has attracted much attention recently in nearly all fields of chemistry due to substantial enhancements in reaction rates. However, the intrinsic nature of the effects of MW irradiation on chemical reactions remains unclear. Herein, the highly effective conversion of NO and decomposition of H2S via MW catalysis were investigated. The temperature was decreased by several hundred degrees centigrade. Moreover, the apparent activation energy (Ea’) decreased substantially under MW irradiation. Importantly, for the first time, a model of the interactions between microwave electromagnetic waves and molecules is proposed to elucidate the intrinsic reason for the reduction in the Ea’ under MW irradiation, and a formula for the quantitative estimation of the decrease in the Ea’ was determined. MW irradiation energy was partially transformed to reduce the Ea’, and MW irradiation is a new type of power energy for speeding up chemical reactions. The effect of MW irradiation on chemical reactions was determined. Our findings challenge both the classical view of MW irradiation as only a heating method and the controversial MW non-thermal effect and open a promising avenue for the development of novel MW catalytic reaction technology.

Microwave catalytic effect: a new exact reason for microwave-driven heterogeneous gas-phase catalytic reactions

Direct catalytic NO decomposition was drastically enhanced under microwave irradiation. Such enhancements would NOT be simply caused by the “hot-spots” hypothesis, as the apparent activation energy decreased greatly under microwave irradiation. Therefore, the microwave catalytic effect rather than solely the “hot-spots” hypothesis is the new exact reason for these enhancements.

Microwave Irradiation Coupled with Physically Mixed MeOx (Me=Mn, Ni) and Cu‐ZSM‐5 Catalysts for the Direct Decomposition of Nitric Oxide under Excess Oxygen

The direct catalytic decomposition of NO into N2 and O2 with high activity and N2 selectivity at low temperature under excess oxygen is a challenge. Herein, we report a new approach for the direct decomposition of NO into N2 and O2 by microwave catalysis over MeOx‐Cu‐ZSM‐5 (Me=Mn, Ni) under excess oxygen. We observed that the microwave direct catalytic decomposition of NO over MeOx‐Cu‐ZSM‐5 under excess oxygen is highly efficient, and the NO conversions are 94.3 % over MnO2‐Cu‐ZSM‐5 at 300 °C and 92.3 % over Ni2O3‐Cu‐ZSM‐5 at 350 °C. Meanwhile, the N2 selectivity remains more than 98 %. Importantly, the apparent activation energies of MnO2‐Cu‐ZSM‐5 and Ni2O3‐Cu‐ZSM‐5 are as low as 15.5 and 25.7 kJ mol−1, which suggests a significant microwave catalytic effect. Furthermore, microwave irradiation exhibits a microwave selective effect. The oxygen concentration has almost no influence on the activity of catalytic decomposition of NO over MeOx‐Cu‐ZSM‐5 under microwave irradiation.

Highly Effective Direct Decomposition of Nitric Oxide by Microwave Catalysis over BaMeO3 (Me=Mn, Co, Fe) Mixed Oxides at Low Temperature under Excess Oxygen

The direct catalytic decomposition of NO with high activity and N2 selectivity is a great challenge at low temperature under excess oxygen. Herein, we report the NO decomposition by microwave catalysis over BaMeO3 (Me=Mn, Co, Fe) mixed oxides for the first time at low temperature under excess oxygen, for which the BaCoO3 catalyst has an outstanding activity with a high NO conversion and N2 selectivity up to 99.8 % and 99.9 %, respectively, even at 250 °C. Comparatively, the best NO conversion is 93.7 % for BaMnO3 and only 64.1 % for BaFeO3 under microwave irradiation. H2 temperature‐programmed reduction, O2 temperature‐programmed desorption, and the microwave‐absorbing properties of the mixed oxides were characterized to illustrate possible reasons that cause such clear differences in the catalytic performance. Importantly, the apparent activation energies for BaMnO3, BaCoO3, and BaFeO3 are as low as 33.4, 13.7, and 46.7 kJ mol−1, respectively, which suggests a significant microwave catalytic effect.