CO2 reforming of CH4 over structured Ni-based catalysts

Abstract

The aim of this study was to contribute to the development of an economical CDRM process requiring less amount of energy and utilizing cheaper, more active and more stable catalyst. For this purpose, the photocatalytic assistance in CDRM process over Ni-Co impregnated MgO, ZnO and TiO2 were tested first at 0-500 °C under UV and visible light in a photocatalytic reaction system. However, no considerable CH4 or CO2 conversion was obtained even if TiO2 photocatalyst was tried to be improved by the addition of dye or organolead perovskite sensitizers to increase its visible light sensitivity. The study was proceeded with the use of various structured Ni-based catalysts such as wash-coated MgO, CeO2 or SiO2 over monoliths, NixCo3-xO4 nanowires and Ni-based nanorods due to their low pressure drop and high surface area. The performance tests of structured Ni-based catalysts were done at a temperature range from 600 °C to 900 °C with various gas hourly space velocities (GHSV) and CH4/CO2 ratios. SEM-EDX, XRD and XPS studies were also performed to understand the surface morphology of the catalysts. The results showed that 8wt.%Ni-2wt.%Co over MgO wash-coated monolith structure led to higher CH4 and CO2 conversions as well as closer H2/CO product ratio to one compared to particulate MgO catalysts and CeO2 or SiO2 wash-coated monoliths. SEM-EDX and XPS results of 8wt.%Ni- 2wt.%Co over MgO wash-coated monolith catalyst spent at 750 °C also showed considerable amount of coke formation; however, the use of 3% oxygen in the feed suppressed the coke formation significantly. The catalyst was stable for 48 h in the presence of O2 added feed (3%) over 42000 mlgcat -1h-1 at CH4/CO2 feed ratio of one and 750 °C. NixCo3-xO4 nanowire structures also showed high catalytic activity at the same conditions; however, they were not stable even under the O2 added feed. The addition of Pd to this catalyst did not improve its stability either. The performance test of Ni-based MgO nanorods and their coated form over monolith was also tested. Although they resulted lower catalytic activity than Ni-based MgO wash-coated monolith, they seemed to be more resistant to coke formation as the SEM analysis indicated.