Ruiyi Yan

Gold nanoparticles supported on Ce–Zr oxides for the oxidative esterification of aldehydes to esters

Au nanoparticles supported on Ce–Zr oxides were prepared and characterized in order to study the role of the support in the oxidative esterification of aldehydes in the presence of molecular oxygen. Ce–Zr solid solutions were synthesized by using (NH4)2Ce(NO3)6 as a precursor, while the mixed oxides were obtained by using a Ce(NO3)3 precursor. The solid solutions exhibited a smaller crystallite size, higher BET surface area, larger amount of H2 consumption, and higher acidity and basicity than the mixed oxides at the same Ce/Zr molar ratio due to the incorporation of Zr4+ into the ceria lattice. The effect of the support was investigated because all the samples presented similar Au particle sizes, as confirmed by the HAADF-STEM study. Supports with higher reducibility showed better performance by activating methanol to methoxy and facilitating the β-H elimination of hemiacetal. We also found that the formation of hemiacetal was enhanced by the acidic sites and basic sites of Au catalysts supported on solid solutions possessing similar reducibility. A plausible reaction mechanism for the oxidative esterification of aldehydes on Ce–Zr solid solution-supported Au nanoparticles was proposed. The screened catalyst was also applicable to the oxidative esterification of different benzylic aldehydes, producing high yields. This catalyst could be reused after a simple separation eight times, keeping a high selectivity of above 99%.

Modified extra-large mesoporous silica supported Au–Ni as a highly efficient catalyst for oxidative coupling of aldehydes with methanol

Herein, we report for the first time that a La–Mg composite oxide modified extra-large mesoporous FDU-12 supported Au–Ni bimetallic catalyst exhibits excellent performance for oxidative coupling of aldehydes (including benzyl and aliphatic aldehydes) with methanol to directly produce methyl esters.

Promoting effects of MgO, (NH4)2SO4 or MoO3 modification in oxidative esterification of methacrolein over Au/Ce0.6Zr0.4O2-based catalysts

MgO, (NH4)2SO4 or MoO3-modified Ce0.6Zr0.4O2-supported gold catalysts were synthesized and studied for the oxidative esterification of methacrolein with methanol to methyl methacrylate. Although the particle size distribution and oxidative state of the supported Au showed almost no change before and after Ce0.6Zr0.4O2 modification as confirmed by TEM, Raman and XPS technologies, all of the modified Au/Ce0.6Zr0.4O2 catalysts demonstrated highly improved catalytic activities. H2-TPR patterns indicated that the amounts of low-temperature active oxygen species increased in the MgO- and MoO3-modified catalysts. At the same time, the strong interaction between gold and Ce–Zr oxides in the MgO-modified catalyst and the charge transfer between Mo6+ and Ce3+ in the MoO3-modified catalyst were evidenced by XPS characterization. Based on the enhanced synergetic effects between the Au nanoparticles and the support for oxygen activation, the MgO-promoted Au catalyst presented the best performance with a methacrolein conversion of 98% and a methyl methacrylate selectivity of 90% in the absence of a base at 80 °C for 2 h of reaction. Differing from MgO and MoO3, (NH4)2SO4 modification simultaneously increased the acid–base properties of the catalyst and then increased the activity of the catalyst due to the promoted formation of the intermediate hemiacetal.

Numerical simulation of CO2-ionic liquid flow in a stirred tank

Ionic liquids (ILs) are new solvents that represent a breakthrough for absorption and conversion of CO2. However, there has been little research on the hydrodynamics of gas-IL systems in stirred tanks, and this has become a bottleneck for development of IL-based reactors. In the present study, a CO2-IL ([bmim][BF4]) flow in a stirred tank was studied using computational fluid dynamics (CFD). A new drag coefficient model that is specific to a gas-ionic liquid system and a population balance model (PBM) were adopted to describe the bubble behavior, such as gas holdup and bubble size evolution, precisely. The predicted results for the total gas holdup and local Sauter diameter agree well with the experimental data. The influences of the gassing rate, agitation speed, and temperature on local gas holdup, bubble size distribution, and interfacial area for the CO2-[bmim][BF4] system were also investigated. The results of this study provide fundamental information for designing gas-IL systems for stirred tanks.

Multi-scale promoting effects of lead for palladium catalyzed aerobic oxidative coupling of methylacrolein with methanol

A highly efficient Pd2Pb8/alumina catalyst was prepared, which provided the highest turnover number (TON) of 302 for aerobic oxidative coupling of methylacrolein with methanol. The enhanced catalytic efficiency could be attributed to the multi-scale (micron, nano and atom scales) promoting effects of the pre-loaded Pb species.

Silica Supported Heteropoly Catalysts for Oxidation of Methacrolein to Methacrylic Acid

The Cu2+ or Fe3+ substituted Cs2HPMo12O40 was synthesized to study the effect of transitional metal cations on selective catalytic oxidation of methacrolein by polyoxometalates. Adding of Cu2+ could reduce acidity and enhance oxidizing ability of the catalyst. The catalytic experiments showed that the addition small amount of Cu2+ to the catalyst could increase the conversion of methacrolein from 65% to 96% and the selectivity to methacrylic acid to 55%, at 300-340°C. It is found adding of Cu2+ could promote the reduction process of catalysts should be the main reason of the performance enhancement. Adding of Fe3+ to the catalyst could induce some new weak acidic sites due to the formation of iron aqua complexes. Whereas, Fe3+ had no significant effect on redox ability of the catalyst. The conversion of methacrolein could reach 96% with the existence of Fe3+. However, the addition of Fe3+ had no significant effect on selectivity to methacrylic acid.