Continuous dimethyl carbonate synthesis from CO2 and methanol over BixCe1−xOδ monoliths: Effect of bismuth doping on population of oxygen vacancies, activity, and reaction pathway

Abstract

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.

Insight into Au/ZnO catalyzed aerobic benzyl alcohol oxidation by modulation–excitation attenuated total reflection IR spectroscopy

“…5f–j, and the C–C bonds of alcohol and aldehyde obviously appear at 1205 and 1201 cm −1 in the liquid phase, respectively. 31 The band at 1081 cm −1 corresponding to aldehyde specifically (C–H) bending of the phenyl ring 34 is more clear and sharp in the liquid phase. The modes at 1038 and 1018 cm −1 decreased dramatically with the increasing band at 1081 cm −1 , depicting the conversion of benzyl alcohol and the formation of benzaldehyde.…”

“…4,33 A new small band appearing at 1081 cm −1 is attributed to in-plane bending of the phenyl (C–H) group of benzyl aldehyde (PhCHO*). 31 A sharp band at 1205 cm −1 corresponds to the υ (C–C) mode, and the lower frequency side appearing at 1201 cm −1 belongs to benzaldehyde, whereas the high frequency side is characteristic of benzyl alcohol. 30 The band at 1379 cm −1 is characteristic of the O–H group in-plane bending mode of benzyl alcohol, and the intensity of this band is very weak in the case of Au/ZnO-300, indicating the fast conversion of benzyl alcohol to benzaldehyde.…”

“…The observed BE values at 529.7 eV, 531.0 eV, and 532.2 eV are assigned to O 2− species in the oxygen lattice (O L ), oxygen vacancies or defects (O V ) and chemisorbed or dissociated oxygen (O C ) species, respectively. 30,31 The amount of O C species seems to contribute to the changes in the catalytic activity; Au/ZnO-300(or 350) (annealing at 300 °C and 350 °C in air) with the highest concentration of the chemisorbed or dissociated (O C ) oxygen species showed the best catalytic activity in the aerobic oxidation of benzyl alcohol (Fig. 1).…”

Effect of the Configuration of Copper Oxide–Ceria Catalysts in NO Reduction with CO: Superior Performance of a Copper–Ceria Solid Solution

“…In previous studies, the formation and accumulation of carbonate on the active sites of the ceria-based catalysts were considered as the main factor leading to deactivation of these catalysts. , Thus, we applied CO 2 -TPD to investigate the basic properties of CuCeO x and CuO/CeO 2 catalysts; Figure d shows that both samples gave rise to an intensive peak at ∼99 °C, which is assigned to the weak basic sites of CuCeO x and CuO/CeO 2 . Interestingly, CuCeO x showed a weak peak at ∼374 °C, belonging to medium basic sites, while no desorption peak was observed at a higher temperature.…”

Recent Advances in Aerobic Photo-Oxidation over Small-Sized IB Metal Nanoparticles

“…In recent decades, well-defined IB metal nanoclusters (NCs) have been documented as novel and promising model catalysts owing to their unique electronic configuration [1][2][3][4][5]. For example, Au/Ag NCs show intrinsically different catalytic behaviors in comparison with conventional gold or silver nanoparticles (Au/Ag NPs) [6][7][8][9][10], which results in superior catalytic properties in many organic reactions, such as selective oxidation and hydrogenation and carbon-carbon couplings. Furthermore, the metal NCs with a nanometric size (1-2 nm) exhibit a non-metallic property with energy quantization manifested in their HOMO-LUMO gap, which is opposite to the localized surface plasmon resonance (LSPR) of conventional metal NPs [11,12].…”