Catalyst Deactivation and Regeneration Processes in Biogas Tri-Reforming Process. The Effect of Hydrogen Sulfide Addition

Urko Izquierdo,Ángel Gutierrez,José Cambra,Juan Arraibi,Victoria Barrio,Iker García-García,Pedro Arias

doi:10.3390/catal8010012

Abstract

This work studies Ni-based catalyst deactivation and regeneration processes in the presence of H2S under a biogas tri-reforming process for hydrogen production, which is an energy vector of great interest. 25 ppm of hydrogen sulfide were continuously added to the system in order to provoke an observable catalyst deactivation, and once fully deactivated two different regeneration processes were studied: a self-regeneration and a regeneration by low temperature oxidation. For that purpose, several Ni-based catalysts and a bimetallic Rh-Ni catalyst supported on alumina modified with CeO2 and ZrO2 were used as well as a commercial Katalco 57-5 for comparison purposes. Ni/Ce-Al2O3 and Ni/Ce-Zr-Al2O3 catalysts almost recovered their initial activity. For these catalysts, after the regeneration under oxidative conditions at low temperature, the CO2 conversions achieved—79.5% and 86.9%, respectively—were significantly higher than the ones obtained before sulfur poisoning—66.7% and 45.2%, respectively. This effect could be attributed to the support modification with CeO2 and the higher selectivity achieved for the Reverse Water-Gas-Shift (rWGS) reaction after catalysts deactivation. As expected, the bimetallic Rh-Ni/Ce-Al2O3 catalyst showed higher resistance to deactivation and its sulfur poisoning seems to be reversible. In the case of the commercial and Ni/Zr-Al2O3 catalysts, they did not recover their activity.

Highlights

Nowadays fossil fuels are still the main contributor to the energy mix, all countries need a sustainable, clean, safe, reliable and guaranteed energy supply
These results were again reproduced by all the catalysts under investigation by reaching very high conversions, near to the ones predicted by thermodynamic equilibrium
After one hour of stable operation under tri-reforming conditions, different H2 S concentrations were continuously added to the system

Summary

Introduction

Nowadays fossil fuels are still the main contributor to the energy mix, all countries need a sustainable, clean, safe, reliable and guaranteed energy supply. Biogas provides solutions to the problems associated with the use of fossil fuels as well as to the ones derived from increasing energy consumption [3,4]. There are many problems for the transportation sector, such as the lack of regulations to access the natural gas grids, or the decentralized production of the biogas [7,8]. In this sense, biogas can be used to produce a clean energy vector for Catalysts 2018, 8, 12; doi:10.3390/catal8010012 www.mdpi.com/journal/catalysts.

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