Sequential Addition of K and ZrO 2 Promoters in Red Mud Catalysts: Implications for CO 2 Hydrogenation to Methane

ABSTRACT Catalytic hydrogenation of CO 2 is an important approach for reducing greenhouse gas emissions and producing value‐added chemicals. Red mud (RM), an industrial waste, has the potential to serve as a cost‐effective catalytic support. This work examines how the consecutive impregnation of a potassium promoter (K, from KNO 3 ) and ZrO 2 onto an RM support affects CO 2 hydrogenation. A series of catalysts was prepared in reverse order of addition: 20%ZrO 2 /3%K/RM (where K was impregnated before ZrO 2 ) and 3%K/20%ZrO 2 /RM (where K was impregnated after ZrO 2 ). These materials were analyzed using XRD, SEM, elemental mapping, TEM, BET, and XRF methods. Catalytic performance was tested at 375 °C and 30 bar pressure, using a CO 2 :H 2 ratio of 1:3. The 20%ZrO 2 /3%K/RM catalyst converted 31% CO 2 with 68% selectivity for methane (CH 4 ). While the 3%K/20%ZrO 2 /RM catalyst had somewhat lower CO 2 conversion (29%), it had much greater CH 4 selectivity (87%). The promoter and support modification sequence significantly impacts catalytic activity and product selectivity in CO 2 hydrogenation over RM‐based catalysts.