Sequential Addition of K and ZrO₂ Promoters in Red Mud Catalysts: Implications for CO₂ Hydrogenation to Methane

Catalytic hydrogenation of CO₂ 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 KNO₃) and ZrO₂ onto an RM support affects CO₂ hydrogenation. A series of catalysts was prepared in reverse order of addition: 20%ZrO₂/3%K/RM (where K was impregnated before ZrO₂) and 3%K/20%ZrO₂/RM (where K was impregnated after ZrO₂). 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 CO₂:H₂ ratio of 1:3. The 20%ZrO₂/3%K/RM catalyst converted 31% CO₂ with 68% selectivity for methane (CH₄). While the 3%K/20%ZrO₂/RM catalyst had somewhat lower CO₂ conversion (29%), it had much greater CH₄ selectivity (87%). The promoter and support modification sequence significantly impacts catalytic activity and product selectivity in CO₂ hydrogenation over RM-based catalysts.