Synthesis and characterization of H3PW12O40/Ceo.1Ti0.9O2 for dimethyl carbonate formation via Methanol carbonation

Ce(0.1)Ti(0.9)O(2)and H3PW12O40/Ce0.2Ti0.9O2 catalysts were synthesized with a sol-gel method to form dimethyl carbonate (DMC) at reaction temperatures T = 110, 170, and 220 degrees C and volumetric flow-rate ratios CO2/N-2 = 1/4, 1/7, and 1/9. The zeolite-like properties of H3PW12O40/Ce0.1Ti0.9O2 with an organized Keggin heteropolyacid structure were demonstrated from X-ray diffraction patterns and Fourier transform infrared spectra. P-31 nuclear magnetic resonance spectra indicated that the Keggin heteropolyacid structure was formed through the addition of heteropoly acid (H3PW12O40). The bond lengths between titanium (Ti(IV)) and its adjacent atoms in the first shell (Ti -O) of Ce0.1Ti0.9O2 and H3PW12O40/Ce0.1Ti0.9O2 were 1.90 and 1.86 (A) over circleA, respectively, confirmed with EXAFS spectra. At 170 degrees C and CO2/N-2 = 1/7, the optimal methanol conversion (5.5%), DMC selectivity (91.4%), and DMC yield (5.0%) of H3PW12O40/Ce0.2Ti0.9O2 were greater than those of Ce0.1Ti0.9O2. Linear regressions of the pseudo -first -order model indicated that the largest rate constant (4.16 x 10(-3) min (-1)), turnover number (TON = 29.07), and turnover frequency (TOF = 4.85 x 10(-2) min (-1)) of DMC formation were obtained with H3PW12O40/Ce0.1Ti0.9O2 at 170 C and CO2/N-2 = 1/7. A reaction mechanism induced by oxygen vacancies over the surfaces of Ce0.2Ti0.9O2 and H3PW12O40/Ce0.1Ti0.9O2 is proposed to describe the formation of DMC. (C)2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.