Impact of potassium promoter amount in Ni catalysts supported on CaAl4O7 for methane reforming with CO2

Calcium aluminate (CaAl4O7 or CA2) prepared by a surfactant assisted (PEG-PPG-PEG, MW:5800) co-precipitation method were employed as catalyst support for potassium modified (1–3% wt.%) 7 wt% nickel catalysts in reforming of methane with carbon dioxide. The X-ray diffraction (XRD), nitrogen adsorption analysis, H2 chemisorption, temperature programmed reduction (TPR) and oxidation (TPO) and scanning electron microscopy (SEM) techniques were used to charactrize the fresh and spent catalysts. The catalytic activity results revealed relatively high conversions (CH4 and CO2) and stability for all the K2O modified catalysts. About 2–6% decrease of CH4 conversion was observed after promotion of 7%Ni/CA2 with K2O. The decrease was attributed to increase in Ni particle size or decrease in Ni dispersity, which caused reduction of available active site for the DRM reaction. Among the promoted catalysts 7%Ni–1%K2O catalyst with 62% CH4 conversion at 700 °C showed highest catalytic activity. K2O promoter increased CO2 affinity, coke resistance and CO2 coke gasification rates of catalysts. After 5 h on stream the TPO analysis of spent catalysts revealed lower carbon deposition with increase of K2O loading from 1 to 3%. 7%Ni–3% K2O showed 45 % decrease in carbon deposition compared to unmodified catalyst. TPO analysis detected atomic, fibrous and graphitic carbon deposition over spent catalysts, with filamentous type as the major type. SEM results only detected fibrous carbon for modified and unmodified spent catalysts.