Conversion of oxygenates derived from biomass is a promising strategy for the production of fuels and chemicals. The needed H 2 can be supplied simultaneously (and sustainably) via aqueous phase reforming (APR; C n H 2n O n + nH 2 O → nCO 2 + 2nH 2 ). APR is typically carried out over supported metal catalysts under liquid water. Dehydrogenation is the first constituent reaction in APR and involves both C−H and O−H bond cleavages; however, details about the mechanism and natures of the active sites remain unknown. Herein, such details are provided for methanol dehydrogenation over a supported Pt/Al 2 O 3 catalyst. Using density functional theory calculations, we find that methanol dehydrogenation occurs on the Pt terraces and at the Pt/Al 2 O 3 interfaces but follows different paths: on interfacial sites, O−H cleavage occurs first and dehydrogenation follows a methoxy route, whereas on terrace sites, C−H cleavage occurs first and dehydrogenation follows a hydroxymethyl route.
Aiming to elucidate guest-induced structural changes in the coordination polymer CPL-2, grand canonical Monte Carlo (GCMC) simulations were used to predict CO loadings in this material, and the results were compared with experimental isotherms. Our calculations suggest that CPL-2 exhibits more pronounced CO-induced structural changes than previously reported. As the initial evidence, the isotherm simulated in the previously reported CPL-2 structure (experimentally resolved from X-ray diffraction in the "as-synthesized" CPL-2) underestimated the measured CO loadings at high pressure, indicating that CPL-2 might undergo structural changes that enable higher pore volumes at high pressure. GCMC simulations in CPL-2 structures considering moderate unit cell expansions reported in the literature still underestimated high-pressure experimental loadings. However, considering an incremental rotation of the CPL-2 bipyridyl pillars with increasing CO pressure, we were able to trace the measured isotherm with the simulation data. Computational analysis shows that ligand rotation in CPL-2 enables higher pore volumes, which, in turn, accommodate more CO as the gas pressure increases. Desorption measurements suggest that hysteresis in the CO isotherm of CPL-2 may also be linked to ligand rotation, and the measured adsorption/desorption cycles show that the rotation is reversible. Based on our simulations for CPL-4 and CPL-5 and previously reported experimental data, it is likely that these materials, which differ from CPL-2 in the bipyridyl ligand, behave similarly in the presence of CO. Our results help understand the behavior of these materials, which present the kind of structural changes that could be potentially exploited to enhance the CO working capacity of ultra-microporous materials for carbon capture applications.
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