The promotional effect of Ca, Mg, and Rh on the activity of Ni-based catalysts from hydrotalcite precursor for dry reforming of methane

Abstract

The world strives towards a way to decrease CH4 and CO2 emissions to the atmosphere. A way to do this is to utilize these gases in processes that can make useful products. One of these are dry reforming of methane (DRM), where CH4 and CO2 are used to produce syngas with a H2/CO ratio of approximately 1. The goal of this thesis was to prepare six catalysts derived from hydrotalcite (HT) precursors, similar to hydrotalcites (HTs) with alkaline earth or noble metal promoters and use them in the DRM reaction while studying their activity, selectivity and stability. Four HT catalysts with calcium (Ca) and magnesium (Mg) as promoters were prepared with the coprecipitation method. In addition, two catalysts were prepared by adding rhodium (Rh) to the Mg catalysts with the incipient wetness method utilising the memory effect of HTs. The catalysts were characterized by N2 adsorption/desorption, temperature programmed reduction (TPR), temperature programmed desorption (TPD), H2-chemisorption and Xray diffraction (XRD) measurements. The catalysts were studied in a DRM reaction at 750 oC and 1 bar for 15 h time on stream (TOS). The reaction was run over 200 ml/min CH4/CO2 1:1 ratio, giving a gas hourly space velocity of 240000 ml gcat h . The NiMgAl catalysts had high initial activities but experienced a rapid decrease in CH4 and CO2 conversions. The most stable catalysts were the NiMgAlRh catalysts, that showed good stability for CH4 and CO2 conversions with very little deactivation, due to the noble metal addition. The NiCaAl catalysts also demonstrated stable activity, ascribed to the CO2 adsorption capacity of Ca, which could gasify deposited carbon.