Nanosheet-Like Ho2O3 and Sr-Ho2O3 Catalysts for Oxidative Coupling of Methane

Yuqiao Fan,Zi Gao,Weiming Hua,Changxi Miao,Yinghong Yue

doi:10.3390/catal11030388

Abstract

In this work, Ho2O3 nanosheets were synthesized by a hydrothermal method. A series of Sr-modified Ho2O3 nanosheets (Sr-Ho2O3-NS) with a Sr/Ho molar ratio between 0.02 and 0.06 were prepared via an impregnation method. These catalysts were characterized by several techniques such as XRD, N2 adsorption, SEM, TEM, XPS, O2-TPD (temperature-programmed desorption), and CO2-TPD, and they were studied with respect to their performances in the oxidative coupling of methane (OCM). In contrast to Ho2O3 nanoparticles, Ho2O3 nanosheets display greater CH4 conversion and C2-C3 selectivity, which could be related to the preferentially exposed (222) facet on the surface of the latter catalyst. The incorporation of small amounts of Sr into Ho2O3 nanosheets leads to a higher ratio of (O− + O2−)/O2− as well as an enhanced amount of chemisorbed oxygen species and moderate basic sites, which in turn improves the OCM performance. The optimal catalytic behavior is achievable on the 0.04Sr-Ho2O3-NS catalyst with a Sr/Ho molar ratio of 0.04, which gives a 24.0% conversion of CH4 with 56.7% selectivity to C2-C3 at 650 °C. The C2-C3 yield is well correlated with the amount of moderate basic sites present on the catalysts.

Highlights

The present energy crisis, owing to the dwindling petroleum resource and its nonrenewable feature, must be solved as soon as possible
Ho2 O3 nanosheets were synthesized by a hydrothermal method reported by Lee and co-workers [61]
We developed Ho2 O3 and Sr-Ho2 O3 nanosheet catalysts for low-temperature

Summary

Introduction

The present energy crisis, owing to the dwindling petroleum resource and its nonrenewable feature, must be solved as soon as possible. As a major component of natural gas, coal-bed gas, and shale gas, is attracting increasing attention as a clean fossil energy and a raw material for producing chemicals. Methane conversion can proceed via nondirect and direct routes [1,2,3,4,5,6,7]. The oxidative coupling of methane (OCM) to ethylene and ethane (C2 hydrocarbons) is an indispensable way that has great prospect in the direct conversion of methane into value-added products [5,6,7]. Since 1982 Keller et al [8] first reported the OCM technology, it has attracted more and more attention in catalysis, chemical industry, and oil and gas fields because of its potential economic value and application prospect

Methods

Results

Conclusion