Abstract
Developing dual function materials (DFM) for integrated carbon capture and utilization (ICCU) presents some unique catalyst design challenges such as matching the operating windows of CO2 desorption and catalysis and controlling selectivity during a non-steady-state spillover-reaction sequence. Herein we show that while combining a methanation catalyst (Pd/SiO2) with a suitable adsorbent component (CaO) leads to a DFM capable of directly methanating captured CO2, this is not the case when we incorporate the same adsorbent (CaO) into a methanol synthesis catalyst (Pd/ZnO). We find that the support (SiO2 or ZnO) influences the CO2 desorption temperature of CaO, with CO2 being much more stable (and less reactive) on CaO/ZnO. At the same time, CaO also inhibits the methanol productivity of Pd/ZnO. In order to independently engineer the adsorbent and catalyst we adopted physical mixture and dual bed configurations using CaO/SiO2 as adsorbent and Pd/ZnO as catalyst. However, these configurations yielded no hydrogenation products, suggesting that the surface spillover required for DFM operation is disrupted by the lack of adsorbent/catalyst interfaces. Moreover, under cyclic DFM tests (capture followed by hydrogenation) the active PdZn phase was not stable, deactivating irreversibly under oxidative capture conditions. These findings highlight the need to control adsorbent and catalyst site proximity with greater precision while protecting active alloy phases under dynamic (cyclic) operation when designing DFMs.
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•Combining an adsorbent with a methanol catalyst does not always yield a successful DFM•On PdCaO/ZnO DFMs, CO2 is adsorbed too strongly, desorbing above the PdZn catalytic window•Separation of catalyst and adsorbent in physical mixtures disrupts the spillover of CO2•Ternary PdZn-CaO/SiO2 DFM enables dynamic methanol synthesis from captured CO2, although CO and CH4 production is still favoured.