Search

Mesocellular silica foams (MCFs) with different pore size were synthesized and used as supports for Pt catalysts for enantioselective hydrogenation of ethyl pyruvate. The influences of the pore size of MCFs, the amount of Pt loading and H2 pressure on catalytic performance of cinchonidine-modified Pt/MCFs were investigated. Both activity and enantioselectivity of the Pt/MCF catalyst increased with the increase in the pore size. These results were attributed to the fact that the larger mesopores facilitate intraparticle diffusion of bulky chiral modifier molecules and generate more chirally modified Pt sites. The performances of Pt/MCFs were compared to those of Pt supported on non-porous silica (Pt/SiO2) and commercial Pt/Al2O3 catalysts. The 1 wt% Pt/MCFs showed superior performance than the 1 wt% Pt/SiO2 and the commercial 1 wt% Pt/Al2O3 catalysts. Furthermore, the 0.6 wt% Pt/MCF exhibited higher activity and enantioselectivity than the commercial 5 wt% Pt/Al2O3, one of the most efficient heterogeneous catalysts for this reaction, in spite of a considerably less Pt loading. At optimized reaction conditions, the Pt/MCF catalyst gave enantiomeric excess of 96% at 100% conversion. They also maintained high enantioselectivity during 10 successive reaction cycles, exhibiting high reusability.

Methane activation through oxychlorination is in the spotlight due to the relatively mild reaction conditions at atmospheric pressure and in the temperature range of 450–550 °C. Although CO2 is known to exhibit good activity for methane oxychlorination, significant amounts of by-products such as CO2, CO and carbon deposits are produced during the reaction over CO2. We investigated the effect of iron in FeOx/CO2 catalysts on methane oxychlorination. FeOx/CO2 with 3 wt% iron shows the maximum yield at 510 °C with 23% conversion of methane and 65% selectivity of chloromethane. XRD and H2 TPR results indicate that iron-cerium solid solution was formed, resulting in the production of more easily reduced cerium oxide and the suppression of catalysts sintering during the reaction. Furthermore, the selectivity of by-products decreased more significantly over FeOx/CO2 than cerium oxide, which can be attributed to the facilitation of HCl oxidation arising from the enhanced reducibility of the former sample.

In this work, SAPO-34 and a series of meso-CeAPSO-34(mesoporous cerium incorporated silicoaluminophosphate, X = Ce/Al molar ratio, X = 0, 0.02, 0.05, 0.07, and 0.10) catalysts with different Ce/Al molar ratio(X) were applied for olefin generation, especially propylene. The chloromethane to olefin (CMTO) reaction at 450 °C demonstrated that meso-CeAPSO-34(0.05) catalysts showed stable chloromethane conversion, with the highest propylene selectivity. The CM conversion increased with the introduction of mesoporosity. The mesopore volume increased and the amount of active sites maintained sufficiently high with the incorporation of cerium. The structural stability of the catalysts and the diffusivity of products improved with the addition of proper amount of cerium. In summary, the enhancement of the physicochemical properties of the catalysts played a crucial role in catalytic stability and the selective production of propylene in the CMTO reaction, resulting in stably high CM conversion and the highest propylene selectivity over meso-CeAPSO-34(0.05) catalyst.

In this work, a series of CoAPSO-34(cobaltsilicoaluminophosphate, X = Co/Al, X = 0, 0.02, 0.05, 0.07, and 0.10) catalysts with different Co/Al molar ratio(X) were prepared for use in the chloromethane to olefin (CMTO) reaction to produce light olefins, such as ethylene and propylene. The CMTO reaction at 450 °C showed that CoAPSO-34(0.05) catalyst had the highest chloromethane conversion among the catalysts with a conversion of 78.75 % at the reaction time of 250 min. The catalytic lifetime increased with increasing Co/Al molar ratio up to 0.05 and then decreased with increasing Co/Al molar ratio up to 0.10. The deposition of coke originating from polymethylbenzene species is thought to be the main reason for deactivation of the catalysts. As the molar ratio of Co/Al increased from 0 to 0.05, the amount of acid site increased, although the textural property did not change. However, as the molar ratio of Co/Al increased from 0.05 to 0.10, the BET surface area and pore volume of the catalysts decreased sharply, in addition to the amount of acid sites. Hence, it is concluded that both the acidic properties and textural properties of the catalysts play a crucial role in determining the catalytic activities in the chloromethane to olefin reaction, resulting in the highest chloromethane conversion and light olefin selectivity over CoAPSO-34(0.05).

A novel synthetic route was devised for 4-aminomethyl-3-Z-methoxyiminopyrrolidine methanesulfonate (AMPM), the key intermediate of gemifloxacin, based on chemoselective hydrogenation of the cyano group in 4-cyano-3-methoxyimino-1-(N-tert-butoxycarbonyl)pyrrolidine (CMBP) with minimum reduction of the methyloxime group employing (t-Boc)2O (BOC) as in situ protecting agent. Over Raney nickel or cobalt catalysts, without in situ BOC protection of amine, the side reaction to 4-aminomethyl-3-amino-1-(N-tert-butoxycarbonyl)pyrrolidine (AABP) was extensive by simultaneous hydrogenation of the methyloxime and cyano groups in CMBP, resulting in over-reduction of the desired intermediate, 4-aminomethyl-3-Z-methoxyimino 1-(N-tert-butoxycarbonyl)pyrrolidine (Z-AMBP) all the way to AABP. When in situ BOC protection was performed, the selectivity to the desired 4-(N-tert-butoxycarbonyl)aminomethyl-3-Z-methoxyimino-1-(N-tert-butoxycarbonyl)pyrrolidine (Z-BAMBP) rose to as high as 91% over Raney cobalt by suppressing the...

Chemoselective hydrogenation of 4-cyano-3-methoxyimino-1-(N-tert-butoxycarbonyl)pyrrolidine (CMBP) to 4-aminomethyl-3-Z-methoxyiminopyrrolidine methanesulfonate (AMPM), the key intermediate for gemifloxacin, was investigated over Pd catalysts with in situ acid protection. Addition of more than 1.6 equiv of acidic protons for CMBP was found to drastically elevate both the reaction rate and selectivity to 4-aminomethyl-3-Z-methoxyimino-1-(N-tert-butoxycarbonyl)pyrrolidine (Z-AMBP) over Pd catalyst with a complete suppression of the major side reaction to 4-cyano-3-amino-1-(N-tert-butoxycarbonyl)-3,4-pyrroline (CABP). Methanol as the organic solvent was found to increase the hydrogenation rate greatly compared to other solvents with a negligible decrease of selectivity. The leaching of Pd by acid and consequent accumulation of Pd ion in the reaction mixture was negligible in CMBP hydrogenation. The novel process of chemoselective CMBP hydrogenation in acidic media over Pd catalyst was thus much simpler yet m...