Ajit S. Mamman

Large enhancement in methane-to-syngas conversion activity of supported Ni catalysts due to precoating of catalyst supports with MgO, CaO or rare-earth oxide

Supported nickel catalysts prepared using commercial sintered low surface area porous catalyst carriers (containing SiO2 and/or Al2O3) precoated with MgO, CaO or rare-earth oxide show very much higher activity, selectivity and productivity in methane-to-syngas conversion reactions, than the catalysts prepared using catalyst carriers without any precoating. Among the precoating metal oxides, the best performance is observed for MgO.

Benzylation of benzene by benzyl chloride over Fe-modified ZSM-5 and H-β zeolites and Fe2O3 or FeCl3 deposited on micro-, meso- and macro-porous supports

Abstract A number of Fe-containing solid catalysts, such as Fe-modified ZSM-5 type zeolites (Fe 2 O 3 /H-ZSM-5, SO 4 2− /Fe 2 O 3 /H-ZSM-5, H-FeMFI and H-FeAlMFI), Fe-modified H-β zeolites (Fe 2 O 3 /H-β and SO 4 2− /Fe 2 O 3 /H-β), Fe 2 O 3 supported on meso-porous Si-MCM-41, silica gel or macro-porous silica–alumina commercial catalyst carrier (SA-5205), and FeCl 3 impregnated on 13X zeolite, Si-MCM-41, silica gel or commercial clays––montmorillonite K10 (Mont K10) or kaolin, have been compared for their performance in the benzylation of benzene by benzyl chloride (80 °C). Among these catalysts, the Fe 2 O 3 /H-β (or H-ZSM-5) and FeCl 3 /Mont K10 (or Si-MCM-41) are found to be highly promising ones for the benzylation, even in the presence of moisture. These catalysts can also be reused in the reaction but with reduced activity. No direct relationship is observed between the acidity (measured in terms of ammonia chemisorbed at 50 or 200 °C) and the benzylation activity of the catalysts. The benzylation activity is controlled mainly by the redox properties of the catalyst. The selectivity for diphenyl methane in the benzylation was found to vary from catalyst to catalyst.

Oxidative conversion of methane to CO and H2 over Pt or Pd containing alkaline and rare earth oxide catalysts

A number of Pt (1.0 wt%) and Pd (1.0 wt%) containing alkaline earth oxide (namely, MgO and CaO) and rare earth oxide (namely, La2O3, Pr6O11, Nd2O3, Sm2O3, Gd2O3, Dy2O3 and Er2O3) catalysts have been compared for their performance in the oxidative conversion of methane to CO and H2 at 700 and 800°C and at very low contact time [GHSV = 5.0 (±0.2) × 105 cm3.g−1.h−1]. The catalysts are characterized by their specific surface area and H2 chemisorption at 40°C. Among the Pt- and Pd-containing catalysts, the best performance is shown by Pt/Gd2O3 and Pd/Sm2O3, respectively. These catalysts show high selectivity for CO but low selectivity for hydrogen due to reverse water gas shift reaction. Since alkaline and rare earth oxides are basic in nature, they act not only as a support for dispersing noble metals but also play a significant role in deciding the activity/selectivity of the Pt- or Pd-containing catalysts.

High temperature combustion of methane over thermally stable CoO-MgO catalyst for controlling methane emissions from oil/gas-fired furnaces

In order to control the concentration of methane in the hot (>800°C) flue gases of oil/gas-fired furnaces, complete combustion of dilute methane (5000 ppm in N2-air mixture) over thermally stable CoO-MgO (Co/Mg = 0.5 or 1.0) catalyst (calcined at 950°C, 1200°C and 1400°C) at different space velocities (15000–120000h-1, measured at 0°C and 1 atm pressure) and temperatures (800–1100°C) has been thoroughly investigated. The catalytic combustion was carried out in quartz reactor with a very low dead volume so that the contribution of homogeneous combustion, particularly at higher temperatures, could be kept low. Involvement of lattice oxygen of the catalyst in the methane combustion was confirmed by methane pulse experiments. The catalysts were characterised by XRD, XPS and also for their surface area and reduction by H2 at different temperatures, using pulse technique. Surface area and methane combustion activity of the catalyst is decreased markedly with increasing its calcination temperature. However, the catalyst calcined at a temperature as high as 1400°C, showed a good methane combustion activity. The catalyst was found to exist as a complete solid solution of CoO and MgO. Both the activation energy and frequency factor for the combustion were found to increase markedly with increasing the catalyst calcination temperature. At the higher reaction temperatures and/or lower space velocities, the contribution of homogeneous combustion occurring simultaneously in the voids of the catalyst bed was found to be appreciable. By using the catalyst (calcined at 1200°C) in the combustion, a methane conversion close to 100% could be obtained at a contact time of about 15ms at 950°C. Since, furnace flue gases are at high temperatures and contain enough oxygen, the combustion of methane to CO2 and water at high conversion can be accomplished just by passing the flue gases over the thermally stable CoO-MgO catalyst at a small contact time, depending upon the temperature of the flue gases.