Ammonia pools in zeolites for direct fabrication of catalytic centers

Jie Yao,Shoya Komiyama,Jiaqi Fan,Guohui Yang,Xiaobo Peng,Tiejian Zhao,Xiaobo Feng,Xiaojing Yong,Yingluo He,Zhongshan Guo,Noritatsu Tsubaki,Yan Zeng,Wei Zhang

doi:10.1038/s41467-022-28606-z

Abstract

Reduction process is a key step to fabricate metal-zeolite catalysts in catalytic synthesis. However, because of the strong interaction force, metal oxides in zeolites are very difficult to be reduced. Existing reduction technologies are always energy-intensive, and inevitably cause the agglomeration of metallic particles in metal-zeolite catalysts or destroy zeolite structure in severe cases. Herein, we disclose that zeolites after ion exchange of ammonium have an interesting and unexpected self-reducing feature. It can accurately control the reduction of metal-zeolite catalysts, via in situ ammonia production from ‘ammonia pools’, meanwhile, restrains the growth of the size of metals. Such new and reliable ammonia pool effect is not influenced by topological structures of zeolites, and works well on reducible metals. The ammonia pool effect is ultimately attributed to an atmosphere-confined self-regulation mechanism. This methodology will significantly promote the fabrication for metal-zeolite catalysts, and further facilitate design and development of low-cost and high-activity catalysts.

Highlights

Reduction process is a key step to fabricate metal-zeolite catalysts in catalytic synthesis
We employ a series of zeolites as supports whose pore channels brim with ammonium ions, and disclose that these zeolites enable in situ reduction of supported metal species without using any additional reduction process
Helium gas was used as the sweeping gas, and the sample was reduced by Ammonia pool effect (APE) at 500 °C for 2 h

Summary

Introduction

Reduction process is a key step to fabricate metal-zeolite catalysts in catalytic synthesis. Typical catalytic experiments (including carbonylation of dimethyl ether, synthesis of ethylene by methane coupling, and methanol synthesis from methane oxidation) prove that the metal-zeolite catalysts, fabricated via APE, realize higher catalytic activity and selectivity than those prepared by traditional reduction method (Fig. 1). The H–Cu(X)-MOR(APE) samples, with decreasing Cu contents, showed lower reduction temperature for the low-temperature peaks, indicating easy reduction of the copper species.

Results

Conclusion