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. Bi_xCe_1-xO_δ 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 Bi_xCe_1-xO_δ catalysts was found to be strongly enhanced with increasing O_V concentration. The concentration of oxygen vacancies exhibited a maximum for Bi_0.12Ce_0.88O_δ, 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 ℃ and a gas-hourly space velocity of 2,880 mL·g_cat^-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.

Heteroatom dopants can greatly modify the electronic and physical properties and catalytic performance of gold nanoclusters. In this study, we investigate the catalytic activity of [Au_25-x(PET)_18-xM]NH₃ (PET = 2-phenylethanethiolate, and M = Cu, Co, Ni, and Zn) nanoclusters in aerobic alcohol oxidation. The [Au_25-x(PET)_18-xM]NH₃ nanoclusters are thoroughly characterized by matrix assisted laser desorption ionization (MALDI) mass spectrometry, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and inductively coupled plasma–mass spectrometry (ICP-MS). The XPS analyses suggest that the transition metals strongly interact with the gold atoms of the nanoclusters. The CeO₂-supported nanoclusters show catalytic activity, based on the conversion of benzyl alcohol, in the order, [Au_25-x(PET)_18-xNi] > [Au_25-x(PET)_18-xCu] > [Au_25-x(PET)_18-xZn] > [Au_25-x(PET)_18-xCo]. Regarding product selectivity, the [Au_25-x(PET)_18-xZn] and [Au_25-x(PET)_18-xCo] catalysts preferably yield benzaldehyde, [Au_25-x(PET)_18-xCu] yields benzaldehyde and benzyl acid, and [Au_25-x(PET)_18-xNi] yields benzyl acid. The exposed metal atoms are considered as the catalytic active sites. Also, the catalytic performance (including activity and selectivity) of the [Au_25-x(PET)_18-xM] catalysts is greatly turned and mediated by the transition metal type.