Dopant induced modification of support-surface structure for high throughput conversion of CO in aqueous media

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The paper addresses the structural and catalytic influence of different modifiers on mesoporous TiO2 loaded with Co, Mn, and Pt for aqueous phase Fischer-Tropsch synthesis (AFTS). The catalysts were synthesized in a two-step method; first, the modified TiO2 was prepared by the revised sol–gel method using different precursors of metal oxide. Then the metal precursors were loaded on the modified support using a mechanochemical procedure, a top-down approach. The quick high yield at room temperature without using any organic or inorganic solvent makes this synthesis procedure efficient. The synthesized catalysts were characterized with different techniques, including XRD, BET, XPS, TEM, HRTEM, H2, CO, CO2, NH3-TPD, etc. Under the identical reaction conditions, the rate of CO conversion under aqueous reaction medium follows the trend SiO2 > ZrO2 > TiO2 > Al2O3 > ZnO > MgO for modified TiO2, whereas the selectivity of C5+ hydrocarbons follow SiO2 > ZnO > MgO > TiO2 > Al2O3 > ZrO2 trend at 453 K and 3 MPa pressure. Based on the results obtained, we found that a balanced surface acidity to basicity ratio plays an important role in the activation of CO, followed by its hydrogenation. Moreover, the DFT results show that the CO conversion and hydrogenation are linearly correlated to the CO* + H* adsorption energy over the catalyst surface. Despite the aqueous phase, the rate of CO conversion for Si-Ti catalyst is kinetically determined using different Fischer-Tropsch empirical kinetic models, with negligible dependency on the partial water pressure term.