Natural sand as a non-conventional catalyst for hydrogen production by methane thermo-catalytic decomposition

The thermo-catalytic decomposition of methane is considered a promising process for H-2 production in the carbon constrained world. A durable and cost-effective catalyst is required for practical methane decomposition processes within industrial applications; unfortunately, most catalysts suffer from extensive deactivation because of carbon deposition. To address this issue, this study assessed a low-cost, widely-available material - natural sand - as a non-conventional catalyst with the realization that it contained impurities such as iron oxides which may impart reaction activity. Its interesting performance in the methane decomposition reaction is reported herein and assessed relative to a potential cause of increasing catalytic activity with longer reaction times. One result of possible significance is the development of tubular carbon structures on the sand's surface that grew significantly in diameter and length with longer reaction times. High Resolution Transmission Electron Microscopy (HRTEM) imaging showed that this tubular carbon contained extensive humps on the external surface of the tube walls which grew in prominence with longer reaction times. The humps did not contain iron particles, in contrast to the heads of the tubes, and consisted of highly disordered graphitic layers. Previous research has pointed to the existence of free radicals or unsaturated bonding in these types of disordered layers, which can provide sites for catalytic reactions. Hence, it is proposed that the increasing prominence of the humps as the reaction time was increased, and by extension an increasing number of surface free radicals, was a possible cause for an increasing catalytic activity after the iron particles on the sand surface were covered with carbon and tube growth was initiated. These data are seen as potentially useful for devising alternative approaches to diminish catalytic deactivation during methane conversion to H-2. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.