Acid–Base Catalytic Effects on Reduction of Methanol in Hot Water

Satoshi Inaba

doi:10.3390/catal9040373

Abstract

We have performed a number of quantum chemical simulations to examine the reduction process of methanol in hot water. Methanol is converted into a methane by capturing a hydrogen molecule and leaving a water molecule behind. The required energy for the reduction is too high to proceed in the gas phase. The energy barrier for the reduction of methanol is reduced by the catalytic effect of water molecules when we consider the reduction in aqueous solution. However, the calculated reduction rate is still much slower than that found experimentally. The ion product of water tends to increase in hot water, even though it eventually decreases at the high temperature of supercritical water. It is valuable to consider the acid–base catalytic effects on the reduction of methanol in hot water. The significant reduction of the energy barrier is accomplished by the acid–base catalytic effects due to hydronium or hydroxyde. Mean collision time between a hydronium and a methanol in hot water is shorter than the reduction time, during which a methanol is converted into a methane. The calculated reduction rate with the acid–base catalytic effects agrees well with that determined by laboratory experiments. The present study reveals a crucial role of the acid–base catalytic effects on reactions in hot water.

Highlights

Molecular hydrogen gas detected by Cassini spacecraft indicates water-rock interaction in active hydrothermal systems within Saturn’s icy moon Enceladus [1]
We will show that the energy barrier for the reduction is significantly reduced by the acid–base catalytic effects
We have performed a number of quantum chemical simulations to examine the reduction process of methanol in hot water such as hydrothermal vents

Summary

Introduction

Molecular hydrogen gas detected by Cassini spacecraft indicates water-rock interaction in active hydrothermal systems within Saturn’s icy moon Enceladus [1]. Composition and temperature of the hydrothermal system in Enceladus were estimated using the composition and the size of fine silica dust particles discovered by Cassini [2,3]. Methane might be produced in hydrothermal systems by methanogens [5] or by abiogenic reductive reactions of carbon dioxide. The hydrogen molecules are involved in a sequence of reductive reactions of single carbon compounds and convert dissolved carbon dioxide into methane by mineral catalyzed hydrothermal reactions [8,9,10]. Isotopic labeling of dissolved carbon dioxide is used to identify the source of the produced methane in the hydrothermal conditions [11,12,13]. It was shown that high temperature water is required for the synthesis of methane from dissolved carbon dioxide

Methods

Results

Conclusion