Abstract
The deactivation pattern of a “model” Ni/MgO catalyst in the pre-reforming of n-hexane with steam (T, 450 °C; P, 5–15 bar) is reviewed. The influence of the steam-to-carbon ratio (S/C, 1.5–3.5) on the rate of catalyst fouling by coking is ascertained. Catalyst fouling leads to an exponential decay in activity, denoting 1st-order dependence of the coking process on active sites availability. Hydrogen hinders the coking process, though slight activity decay is due to sintering of the active Ni phase. Deactivation by thiophene causes a sharp, almost linear, drop to nearly zero activity within only 6 h; this deactivation is likely due to dissociative adsorption of thiophene with subsequent strong, irreversible chemical adsorption of S-atoms on active Ni sites, i.e., irreversible poisoning. Modeling of activity decay curves (α, at/a0) by proper kinetic equations allows assessing the effects of temperature, pressure, S/C, H2 and thiophene feed on the deactivation pattern of the model Ni/MgO catalyst by coking, sintering, and poisoning phenomena.
Highlights
There is a strong commitment worldwide to enhance the practical and economical feasibility of the steam reforming (SR) technology through efficiency improvement and feedstock versatility, which could result in significant improvements in fuel processing economy [1,2,3,4,5,6,7]
Only after the pioneering work of Rostrup-Nielsen on the steam reforming of C1-C7 alkanes on magnesia-supported metal catalysts, which led to the development of the SPARG process [2,10,14], has light been shed on the reaction mechanism and kinetics, leading to further improvements in catalysts’ performance [11,14,16,17]
Coking processes on Ni-based catalysts in steam reforming and methanation reactions proceed through common carbon intermediates leading to the formation of several types of deposits depending on operating conditions [2,8,12,13,14,15,18,19,20,21,22,23,24]
Summary
There is a strong commitment worldwide to enhance the practical and economical feasibility of the steam reforming (SR) technology through efficiency improvement and feedstock versatility, which could result in significant improvements in fuel processing economy [1,2,3,4,5,6,7] In this context, pre-reforming constitutes an established technology with economic and operational benefits on the overall syngas production, representing an important tool, especially for the revamping of older SR plants [2,3,4,8,9,10]. Coking processes on Ni-based catalysts in steam reforming and methanation reactions proceed through common carbon intermediates leading to the formation of several types of deposits depending on operating conditions [2,8,12,13,14,15,18,19,20,21,22,23,24]. Previous works) are presented, and the effects of catalyst deactivation on activity, selectivity, and stability are analyzed and discussed
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