Insight on the Interaction of Methanol-Selective Oxidation Intermediates with Au- or/and Pd-Containing Monometallic and Bimetallic Core@Shell Catalysts

Using density functional theory (DFT), the interaction of crucial molecules involved in the selective partial oxidation of methanol to methyl formate (MF) with monometallic Au and Pd and bimetallic Au/Pd and Pd/Au core@shell catalysts is systematically investigated. The core@shell structures modeled in this study consist of Au(111) and Pd(111) cores covered by a monolayer of Pd and Au, respectively. Our results indicate that the adsorption strength of the molecules examined as a function of catalytic surface decreases in the order of Au/Pd(111) > Pd(111) > Au(111) > Pd/Au(111) and correlates well with the d-band center model. The preadsorption of oxygen is found to have a positive impact on the selective partial oxidation reaction because of the stabilization of CH₃OH and HCHO on the catalyst surface and the simultaneous intensification of MF desorption. On the basis of a dynamical matrix approach combined with statistical thermodynamics, we propose a simple route for evaluating the Gibbs free energy of adsorption as a function of temperature. This method allows us to anticipate the relative temperature stability of molecules involved in the selective partial oxidation of methanol to MF in terms of catalytic surface

Dual Functionality of TiO₂/Biochar Hybrid Materials: Photocatalytic Phenol Degradation in the Liquid Phase and Selective Oxidation of Methanol in the Gas Phase

A series of new inorganic–organic hybrid materials based on TiO₂ and new biochar-based supports (biochar obtained by pyrolysis of miscanthus straw pellets (MSP) and soft wood pellets (SWP) at 550 and 700 °C) were successfully prepared using ultrasound-assisted methodology. The resulting composites were characterized by a wide range physicochemical techniques and investigated in water and gas-phase photocatalytic test reactions. Our best composite (TiO₂/SWP700) achieved phenol degradation of 64.1% (under UV light) and 33.6% (under visible light). In addition, it also showed an extraordinarily high activity (∼90%) in selective oxidation of methanol to methyl formate in flow gas phase, high selectivity to methyl formate (∼80%), and high yield of methyl formate (∼88%) after 240 min of illumination. It can be noticed that when TiO₂ is supported on biochar it presented a superior photocatalytic ability and could be recycled at least 5 times in both photocatalytic runs tests with reproducible high photocatalytic efficiency