Fuel, Vol.235, 868-877, 2019
CO2 reforming of methane to syngas at high pressure over bi-component Ni-Co catalyst: The anti-carbon deposition and stability of catalyst
The catalytic performance of Ni-Co bi-component catalysts in CO2 reforming of methane (CRM) under high pressures was studied for obtaining highly stable Ni-based catalysts, which is important for the industrialization of high pressure CRM. A series of 5% (xNiyCo)/SBA-15 catalysts were prepared with a modified co-impregnation method by adding trace amount of beta-cyclodextrin (CD) into Ni(NO3)(2) impregnation solution. The effects of catalyst compositions (Ni/Co ratio) and the CRM reaction conditions (pressure, gas hourly space velocity, time on stream, etc) on the catalysts stabilities were investigated. The carbon deposition behaviors of the catalysts during the high pressure CRM reaction were disclosed through detailed characterizations of the spent catalysts. The type of coke, instead of the amount of deposited carbon, was proved to be responsible for the deactivation of 5% (xNiyCo)/SBA-15 catalysts during the high pressure reaction. The amount of carbon deposition depended strongly on the Co loading in the bimetallic catalysts. Long-term stability with 100 h TOS at 2.0 MPa and 800 degrees C was achieved for the optimized 5% (4.5Ni0.5Co)/SBA-15 catalyst and a slow deactivation (decrease in CH4 conversion) was observed. The reaction results with different reaction time over 5% (4.5Ni0.5Co)/SBA-15 at high pressures suggested that the accumulation of carbon deposition took place mainly at the initial stage of the CRM reaction. Moreover, the disorder degree of deposited carbon species and the sintering of metal particles were identified as the primary reasons for the deactivation of the catalysts. Trace Co enriched on Ni-Co surface of 5% (4.5Ni0.5Co)/SBA-15 suppressed Ni aggregation and facilitated the adsorption of co-reactant.