Post-steam-treatment of Mo/HZSM-5 catalysts: An alternative and effective approach for enhancing their catalytic performances of methane dehydroaromatization

Post-steam-treatment is a facile and effective method for improving the catalytic performances of Mo/HZSM-5 catalysts in methane dehydroaromatization under nonoxidative conditions. The treatment can enhance the stability of the catalyst and also give a higher methane conversion and a higher yield of light aromatics, as well as a decrease in the formation rate of carbonaceous deposits. (27)Al, (29)Si, and (1)H multinuclear magic angle spinning nuclear magnetic resonance, X-ray photoelectron spectroscopy, X-ray diffraction, X-ray fluorescence spectroscopy, and thermogravimetric analysis measurements as well as catalytic reaction evaluations were employed to conduct comparative studies on the properties of the catalysts before and after the post-steam-treatment. The results revealed that the number of free Bronsted acid sites per unit cell decreased, while more Mo species migrated into the HZSM-5 channels for the 6Mo/HZSM-5 catalysts after the post-steam-treatment. In addition, the average pore diameter was also larger for the post-steam-treated catalysts, and this was advantageous for mass transport of the reaction products. However, a severe post-steam-treatment, i.e., with longer treating time, of the 6Mo/HZSM-5 catalyst will lead to the formation of the Al(2)(MoO(4))(3) phases, which is detrimental to the reaction.

The copolymerization of carbon dioxide and propylene oxide with Y(CCl3COO)(3)-diphenylzinc-glycerol catalyst

Various organometallic compounds (diphenylzinc, dibenzylzinc, dicyclohexylzinc, bis( pentafluorophenyl) zinc, diethylzinc, di(n-butyl) zinc, triethylaluminum) were used to form Y(CCl3COO)(3)-organometallic compound-glycerol catalyst for the copolymerization of carbon dioxide and propylene oxide. It was found that Y(CCl3COO)(3)-diphenylzinc-glycerol catalyst showed the highest catalytic activity, at optimum conditions the yield could be as high as 478.8 ( g polymer/mol Zn h).

Rare Earth Pyrophosphates: Effective Catalysts for the Production of Acrolein from Vapor-phase Dehydration of Glycerol

Vapor-phase dehydration of glycerol to produce acrolein was investigated at 320 A degrees C over rare earth (including La, Ce, Nd, Sm, Eu, Gd, Tb, Ho, Er, Tm, Yb, Lu) pyrophosphates, which were prepared by precipitation method. The most promising catalysts were characterized by means of XRD, FT-IR, TG-DTA, BET and NH3-TPD measurements. The excellent catalytic performance of rare earth pyrophosphate depends on the appropriate surface acidity which can be obtained by the control of pH value in the precipitation and the calcination temperature, e.g. Nd-4(P2O7)(3) precipitated at pH = 6 and calcined at 500 A degrees C in the catalyst preparation.

Studies of methane reforming with carbon dioxide on hexaaluminates

In this paper, a series of Sr1-xLaxNiAl11O19 catalysts were synthesized and their chemical and physical properties were investigated by XRD, UV-DRS, H-2-O-2 titration, TPR and Py-IR techniques. The experimental results show that the Sr1-xLaxNiAl11O19 catalysts have a magnetoplumbite structure and Ni ion is shared between tetrahedral and octahedral sites of the spinel blocks, and the amount of nickel ions in the tetrahedral environment increases with the increase of x value in Sr1-xLaxNiAl11O19. The TPR study revealed that the reducibility of the series of the catalysts depends strongly on the substitution value x, that is, a low temperature peak appears for samples without substitution, in case of samples with x = 1 high temperature peak appears, and for samples with 0reforming reaction due to the similar dispersion of Ni particle. Whereas, the substitution has a great effect on the acidity of catalyst, the number of acidic sites and amount of the carbon deposition on the catalyst surface. So it is evident that carbon deposition in carbon dioxide reforming of methane can be suppressed by decreasing the acidity of the complex oxides catalysts.

Studies of methane reforming with carbon dioxide over LaNiAl11O19

A new type of the catalyst, LaNiAl11O19, for the methane reforming with carbon dioxide was synthesized and evaluated. LaNiAl11O19 has a hexaaluminate structure and can keep large surface and heat resistance against sintering at high reaction temperature. As compared with La2O3-Ni/SrAl12O19, in the CH4 + CO2 reaction, LaNiAl11O19 catalyst displays a higher catalytic activity, lower coking amount and excellent sintering resistance of Ni particle, due to its stable structure.

Positional distribution of fatty acids on the glycerol backbone during the biosynthesis of glycerolipids in Ectocarpus fasciculatus

The biosynthesis of glycolipids in E. fasciculatus was studied by C-14 label and chase. The fatty acids in sulphoquinovosyl diacylglycerol (SQDG) were almost 16-carbon and 18-carbon ones. In addition to the two fatty acids, monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG) contained 8.5 mol% and 31.0 mol% of eicosapentaenoic acid (20 : 5), respectively, and this fatty acid was usually distributed in the sn-1 position of the glycerol backbone. When plants were incubated with [2-C-14] acetate, differences existed in the positional distribution of the labeled fatty acids in sn-1 and sn-2 among the three glycerolipids. In SQDG C-14-labeled fatty acids were distributed uniformly in the sn-1 and sn-2 positions. In DGDG, C-14-labeled fatty acids were mainly distributed in the sn-2 position. In MGDG, the radioactivity of fatty acids in sn-1 position was far greater than that in sn-2 position after a 30 min pulse label, and the difference in radioactivity between the two positions decreased rapidly. The above results indicated that differences in the positional distribution of C-14-labeled fatty acids between sn-1 and sn-2 positions might be related to 20 : 5 and the biosynthesis of DGDG. Our results also suggested that E. fasciculatus had the same DGDG biosynthetic pathway as that in higher plants and galactosyl transferase was selective for MGDC.