Abolghasem Shamsi

Catalytic Performance of Pt/ZrO2 and Pt/Ce-ZrO2 Catalysts on CO2 Reforming of CH4 Coupled with Steam Reforming or Under High Pressure

CO2 reforming of methane was performed on Pt/ZrO2 and Pt/Ce-ZrO2 catalysts at 1073 K under different reactions conditions: (i) atmospheric pressure and CH4:CO2 ratio of 1:1 and 2:1; (ii) in the presence of water and CH4:CO2 ratio of 2:1; (iii) under pressure (105 and 190 psig) and CH4:CO2 ratio of 2:1. The Pt supported on ceria-promoted ZrO2 catalyst was more stable than the Pt/ZrO2 catalyst under all reaction conditions. We ascribe this higher stability to the higher density of oxygen vacancies on the promoted support, which favors the cleaning mechanism of the metal particle. The increase of either the CH4:CO2 ratio or total pressure causes a decrease in activity for both catalysts, because under either case the rate of methane decomposition becomes higher than the rate of oxygen transfer. The Pt/Ce-ZrO2 catalyst was always more stable than the Pt/ZrO2 catalyst, demonstrating the important role of the support on this reaction.

Influence of preparative procedure on the activity and selectivity of FeZSM-5 catalysts in syngas conversion

Abstract The ZSM-5 supported iron catalysts have been investigated with respect to physical and chemical properties and to activity and product selectivity for conversion of synthesis gas to hydrocarbon products. The catalyst preparations consisted of (1) direct decomposition of (C5H5Fe(CO)2)2 on ZSM-5, (2) impregnation of ZSM-5 with an aqueous solution of iron nitrate, and (3) physical admixture of precipitated iron oxide with ZSM-5. Some H2 and CO chemisorption studies and magnetization measurements were conducted to measure the average metal crystallite size. At the metal loading of about 8 wt%, the catalysts prepared by the first method produced higher metal dispersion compared to the other two methods of preparation, although the amount of aromatic compounds in liquid hydrocarbon products was very low. Infrared studies of chemisorbed pyridine on these samples indicate that ion exchange of Fen+ for acidic protons occurs in aqueous solution impregnated catalysts, while no ion exchange is found in organometallic impregnated or physically admixed catalysts.

Catalytic cracking of a coal tar in a fluid bed reactor

Abstract A coal-derived tar from the Coal Technology Corporations mild gasification process was catalytically cracked in a fluid bed reactor. Several commercial catalysts were tested and their effectiveness in decomposing tar and releasing sulfur was compared. The effects of process variables such as temperature and residence time were also tested. It was found that the Linde LZ-Y82 zeolite was the most effective catalyst tested in converting tar to coke and gases. LZ-Y82 was also the most effective catalyst in converting the sulfur compounds in the tar into hydrogen sulfide which can be removed by a sorbent. Other catalysts such as LZ-Y82/NiW, LZ-Y82/ZnTi, and Englehards Sp2323 showed strong catalytic activity. LZ-Y3Z7, which is the LZ-Y82 catalyst impregnated with zinc, displayed less activity. LZ-Y82 cracked most effectively in the temperature range 500–530°C.

Oxidative coupling of methane over calcium manganate and gadolinium manganate perovskites promoted with sodium pyrophosphate

Abstract GdMnO3, promoted with Na4P2O7 was found to be an active and selective catalyst for partial oxidation of methane to higher hydrocarbons. A C2-yield of 20% was obtained over this catalyst at 1101 K. There was no appreciable change in both the methane conversion and C2-yield during 26 h of reaction. CaMnO3 promoted with Na4P2O7 was found to be a poor catalyst for C2 formation even though both CaO and manganese oxide promoted with Na4P2O7 were good catalysts for the production of C2 compounds. An X-ray photoelectron spectroscopic analysis showed manganese in both Mn3+ and Mn4+ oxidation states was present on both Na4P2O7/GdMnO3 and Na4P2O7/ CaMnO3. Treatment of the catalyst Na4P2O7/GdMnO3 with helium improved both conversion and C2 selectivity. However, significant changes in the chemical states of sodium, manganese, and phosphorus were not observed on Na4P2O7/GdMnO3 after treating with helium. Thus, it was not feasible to relate the catalytic performance to the chemical states of different species present on the surface. Significant amounts of sodium were retained on the surface of Na4P2O7/GdMnO3 even after 20 h of reaction as observed by Auger electron spectroscopy. The perovskite structure did not affect the catalytic performance of CaMnO3 or GdMnO3 as evidenced by the fact that their respective oxide mixtures (CaO/manganese oxide and Gd2O3/manganese oxide) showed a similar catalytic activity.

Effect of Pressure on Catalyst Activity and Carbon Deposition During CO2 Reforming of Methane over Noble-Metal Catalysts

The reforming of methane with CO2 was studied over 1wt% Rh/alumina, Pt/ZrO2, and Ce-promoted Pt/ZrO2 catalysts at 800°C and pressures of 1, 8, and 14 bar. It was found that high pressure resulted in greater carbon formation, lower methane and CO2 conversions, as well as a lower H2/CO ratio. Temperature-programmed oxidation (TPO), of the catalysts after reaction, shows several CO2 peaks for the Ce-promoted catalyst, indicating several sources or types of carbon and/or several locations on the catalyst are involved with carbon deposition. The change in the temperature and intensity of the TPO peaks with pressure indicates that more stable carbon is deposited at high pressure. Thermodynamic calculations for the endothermic reaction of CH4 with CO2, CH4 decomposition, and CO disproportionation were also performed. The results of these calculations are consistent with CO disproportionation being a larger contributor to carbon deposition at high pressure.

Partial oxidation of13C-labeled ethylene in methane over Ca/Ni/K catalysts

The relative reactivity of ethane and ethylene compared to methane over the Ca/Ni/K catalyst was determined. The reactivities are in the order of ethylene > ethane ≫methane. The catalyst was also studied using temperature-programmed reaction, desorption and decomposition.