Next Article in Journal
Promoting Effects of Copper and Iron on Ni/MSN Catalysts for Methane Decomposition
Next Article in Special Issue
Co-Encapsulation of Rhenium and Ruthenium Complexes into the Scaffolds of Metal–Organic Framework to Promote CO2 Reduction
Previous Article in Journal
The Sonocatalytic Activation of Persulfates on Iron Nanoparticle Decorated Zeolite for the Degradation of 1,4-Dioxane in Aquatic Environments
Previous Article in Special Issue
CO2 to Value-Added Chemicals: Synthesis and Performance of Mono- and Bimetallic Nickel–Cobalt Nanofiber Catalysts
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Enhancing the Activity of Cu-MOR by Water for Oxidation of Methane to Methanol

1
Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
2
State Key Laboratory of Fine Chemicals, The Pennsylvania State University-Dalian University of Technology (PSU-DUT) Joint Center for Energy Research, School of Chemical Engineering, Dalian University of Technology, Dalian 116023, China
3
School of chemical engineering, University of Chinese Academy of Sciences, Beijing 100039, China
*
Authors to whom correspondence should be addressed.
Catalysts 2023, 13(7), 1066; https://doi.org/10.3390/catal13071066
Submission received: 27 May 2023 / Revised: 27 June 2023 / Accepted: 1 July 2023 / Published: 3 July 2023

Abstract

:
As clean energy, methane has huge reserves and great development potential in the future. Copper zeolites are efficient in the oxidation of methane to methanol. Water has been confirmed as a source of oxygen to regenerate the copper-zeolite active sites to enable selective anaerobic oxidation of methane to methanol. In this work, we report that the methanol yield increased from 36 μmol/g (Cu-MOR1) to 92 μmol/g (Cu-MOR1-water) as a result of water enhancing the activity of copper ion-exchange mordenite catalyst. We show for the first time that water could convert inactive copper species into active copper species during catalyst activation. A combination of the XPS, FTIR, and NMR results indicates that water dissociates and then converts ZCuIIZ into ZCuII(OH) (where Z indicates framework O (Ofw) bonded to one isolated Al in a framework T-site, i.e., 1Al) and simultaneously produces a Brönsted acid site during catalyst activation. This finding can be used to tune the state of copper species and design highly active copper-zeolite catalysts for methane oxidation to methanol.

Graphical Abstract

1. Introduction

Methane is the main component of natural gas and natural gas hydrate, being clean and easy to distribute, and the reserves of natural gas hydrate are huge [1,2]. In recent years, the development of shale gas technology has made methane (CH4) inexpensive and accessible.
Currently, the mainly utilization of methane is combustion for power generation and heating [3]. There are limited industrial routes for converting methane into fuels and chemicals. Methane could be converted to chemicals via both direct and indirect routes. To date, methane is mainly converted to chemicals and fuels through indirect processes. For the indirect process, methane is first converted to syngas (H2 and CO) through a steam reforming process and then the syngas is converted to chemicals such as methanol and gasoline. The steam reforming process operates at high temperatures (700–1000 °C) and pressures (15–40 atm) and is an energy-intensive process, making direct conversion an attractive alternative [3]. The direct conversion of methane to chemicals has been a very active topic in the past few decades. Studies on the direct conversion of methane to chemicals have mainly focused on three processes: oxidative coupling of methane to C2+ carbon species, nonoxidative conversion of methane to aromatics, and partial oxidation of methane to methanol [4,5,6,7,8,9,10]. Oxidative coupling of methane usually requires activation of methane at high temperatures. However, high temperature favors the complete oxidation of methane and C2 (C2H4 and C2H6). The process currently faces two important challenges. The first is catalyst selectivity and the second is catalyst deactivation. To date, despite extensive research, no specific catalyst has fully met the practical industrial and economic requirements. The advantage of the nonoxidative conversion of methane to aromatics is that it prevents irreversible overoxidation, which leads to thermodynamically stable undesired products, such as CO2 and H2O. The nonoxidative conversion of methane to aromatics faces similar challenges to the oxidative coupling of methane. The reaction process requires high temperatures, but the catalyst will deactivate rapidly at high temperatures. Unlike the oxidative coupling of the methane process and the anaerobic conversion of the methane to aromatics process, the m