Modified Cu–Zn–Al mixed oxide dual function materials enable reactive carbon capture to methanol†

Abstract

Reactive carbon capture (RCC), an integrated CO₂ capture and conversion process that does not require generating a purified CO₂ stream, is an attractive carbon management strategy that can reduce costs and energy requirements associated with traditionally separate capture and conversion processes. Dual function materials (DFMs) comprised of co-supported sorbent sites and catalytic sites have emerged as a promising material design to enable RCC. DFMs have been extensively studied for methane production, but the noncompetitive economics of methane necessitates the development of DFMs to target more valuable, useful, and versatile products, like methanol. Herein, we report the development of modified Cu–Zn–Al mixed oxide (Alk/CZA, Alk = K, Ca) DFMs for combined capture and conversion of CO₂ to methanol. CO₂ chemisorption, in situ DRIFTS characterization, and co-fed hydrogenation performance revealed that K and Ca have different effects on the CO₂ capture and catalytic behavior of the parent CZA. K-modification resulted in the greatest promotional effect on capture capacity but the most detrimental effect on co-fed hydrogenation catalytic activity. Interestingly, when used in a cyclic temperature-and-pressure-swing RCC operation, K/CZA exhibited a greater conversion of adsorbed CO₂ (94.4%) with high methanol selectivity (46%), leading to greater methanol production (59.0 μmol g_DFM⁻¹) than the parent CZA or Ca/CZA (13.2 and 18.9 μmol g_DFM⁻¹, respectively). This study presents the foundational methodology for the design and evaluation of novel DFMs to target renewable methanol synthesis, highlighted by a critical learning that co-fed CO₂ hydrogenation performance is not an effective indicator of RCC performance.