We evaluated bismuth doped cerium oxide catalysts for the continuous synthesis of dimethyl carbonate (DMC) from methanol and carbon dioxide in the absence of a dehydrating agent. BixCe1−xOδ nanocomposites of various compositions (x = 0.06–0.24) were coated on a ceramic honeycomb and their structural and catalytic properties were examined. The incorporation of Bi species into the CeO2 lattice facilitated controlling of the surface population of oxygen vacancies, which is shown to play a crucial role in the mechanism of this reaction and is an important parameter for the design of ceria-based catalysts. The DMC production rate of the BixCe1−xOδ catalysts was found to be strongly enhanced with increasing Ov concentration. The concentration of oxygen vacancies exhibited a maximum for Bi0.12Ce0.88Oδ, which afforded the highest DMC production rate. Long-term tests showed stable activity and selectivity of this catalyst over 45 h on-stream at 140 °C and a gas-hourly space velocity of 2,880 mL·gcat−1·h−1. In-situ modulation excitation diffuse reflection Fourier transform infrared spectroscopy and first-principle calculations indicate that the DMC synthesis occurs through reaction of a bidentate carbonate intermediate with the activated methoxy (−OCH3) species. The activation of CO2 to form the bidentate carbonate intermediate on the oxygen vacancy sites is identified as highest energy barrier in the reaction pathway and thus is likely the rate-determining step.
Synthesis of liquid biofuels (C 11 -C 13 ) from cellulosic ethanol is regarded as a promising and versatile protocol. In this study, oxide-supported nanogold catalysts exhibit good catalytic performance in ethanol conversion with cinnamaldehyde and finally give rise to the C 11 -C 13 hydrocarbon. High selectivity (70%) for C 11 -C 13 hydrocarbons is achieved over Au/NiO via a one-pot cascade reaction, viz. cross-aldol condensations in the presence of oxygen and base (K 2 CO 3 ) and then full hydrodeoxygenation with hydrogen gas. EtOH-TPD and TGA analyses show that the ethanol is activated to acetaldehyde (CH 3 CHO*) over the surface oxygen vacancies of the NiO support. The CH 3 CHO* then reacts with cinnamaldehyde at the interfacial perimeter of the Au/NiO composite during the cascade reactions, as evidenced by comparison of the catalytic performance with that over another oxide-supported Au NP, chemo-adsorption investigations, and in situ infrared spectroscopy investigations. This work may provide new guidelines for designing efficient catalysts to convert bioethanol into biofuels with high energy density. a Reaction conditions: 10 mg of 1 wt% Au catalysts, 26 mL of cinnamaldehyde, 10 mg of base, 3 mL of ethanol, 4 h, and 1 MPa air. b The cinnamaldehyde conversion and product selectivity were determined by GC-MS analysis.3656 | Nanoscale Adv., 2019, 1, 3654-3659This journal is
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