Saad Tahir

A new chemical route for the synthesis of nano-crystalline α-Al2O3 powder

Abstract Nano crystalline α-Al 2 O 3 powders have been prepared by pyrolysis of a complex compound of aluminium with triethanolamine (TEA) and sucrose. The soluble metal ion-TEA complex with sucrose forms the precursor material on complete dehydration. The single-phase α-Al 2 O 3 powder has resulted after heat treatment at 1150°C. The precursors and the heat treated final powders have been characterized by X-ray diffractometry (XRD), differential thermal and thermogravimetric analysis TG/DTA, Infrared spectroscopy (IR) and transmission electron microscopy (TEM). The average particle sizes as measured from X-ray line broadening and transmission electron microscopy studies are around ∼20 nm. The powder which has crystallite sizes of the same order with the particle size indicates the low agglomeration of crystallites.

Catalytic Destruction of Volatile Organic Compound Emissions by Platinum Based Catalyst

Pt/γ-Al2O3 (spheres) catalysts were prepared by depositing a resilient coating of Pt metal on the external surface of the support. Using a bench-scale rig, the developed Pt/Al2O3 catalysts were investigated for their destruction efficiencies with a variety of VOCs in air-streams (VOC concentrations between 600–700 ppm) at space velocities ranging from 13,000 to 20,000 h−1 (flow rates between 865–1335 ml/min) at atmospheric pressure. Catalytic activity was enhanced with an increase of Pt loading on Al2O3 support up to 0.3 % Pt. The 0.3 % Pt/Al2O3 showed above 99 % conversion efficiency and stability with non-halogenated VOCs at inlet reaction temperatures ranging between 196–355 °C, but it was deactivated by destruction of chlorinated VOCs. Ageing the 0.3 % Pt used catalyst at 550 °C for a longer period did not affect its activity. Pretreatment of the 0.3 % Pt developed catalyst with hydrogen also did not improve activity in the destruction of toluene in air, compared to the fresh prepared catalyst.

Catalytic oxidation for air pollution control.

Bench-scale experiments have been conducted to evaluate a series of titania-supported Pt-Pd (as oxides) catalysts in the presence and absence of MoO3 and Fe2O3 additives for their effectiveness in the complete catalytic oxidation of volatile organic compounds (VOCs) in air likely to be found in waste gases. Under oxidizing conditions, all of the catalysts promoted the complete oxidation of VOCs to CO2 and H2O. 99 % Conversion was achieved with a C2H4-C2H6 gas mixture in air at temperatures between about 160–450 °C and at a space velocity of 20,000 h−1. Oxidation activity for the titania supported catalysts were found to decrease in the order Pt-Pd-Mo-Fe > Pt-Pd-Mo > Pt-Pd-Fe > Pt-Pd. However, the addition of MoO3 and Fe2O3 increase the catalyst activity and reduce the reaction temperature for the complete destruction. Ageing was also performed in order to study the stability of the most active catalyst. Pt-Pd-Mo-Fe (as oxides) on titania catalyst is effective in oxidizing a wide range of volatile organic compounds at relatively low temperatures (220–405 °C) and and at a space velocity of 40,000 h−1 and is resistant to poisoning by halogenated and amine volatile organic compounds.

Separation of dichloromethane-nitrogen mixtures by adsorption: experimental and molecular simulation studies

Experimental and grand canonical Monte Carlo simulation results for the separation of a CH2C12 (1.5 mol%)-N2 binary gas mixture in molecular sieve materials are presented. AlPO4-5 and MCM-41 molecular sieves have been used as the selective adsorbents because they consist of uniform arrays of uni-dimensional channels of micro and meso length scales, respectively. Adsorption isotherms were measured at 318 K and at pressures between 50 kPa and 130 kPa. Two MCM-41 materials have been used, one with a 33 A pore diameter and the other with a 42 Á pore diameter. For AlPO4-5 at 110kPa the total amount adsorbed from experiment was found to be independent of equilibration time at 0.0542, 0.0538 and 0.0547 mmol per g AlPO4-5 for 2, 24 and 48 hours, respectively. However, the selectivity for CH2C12 was found to increase with time from 1.29, to 4.59, to 10.74. For MCM-41 at 110kPa the selectivity for CH2C12 was found to be dependent on pore size. On increasing the pore size from 33 Å to 42 Á the selectivity for CH2C12 increased considerably. Grand canonical Monte Carlo simulations agreed qualitatively with the experimental results, showing a greater selectivity for CH2C12 than for N2. The simulations indicate that MCM-41 has a lower selectivity for CH2C12 than A1PO4-5, which contradicts the experimental results. Reasons for these discrepancies are presented and discussed.

Catalytic oxidation of ethane over supported metal oxide catalysts

SnO2 supported metal oxides (metal = Mn, Co, Cu, Ce, Ni) have been prepared by impregnation techniques and investigated for the complete oxidation of 0.2 vol.% ethane in an air stream using a bench scale rig. Mn oxide/SnO2 and Co oxide/SnO2 proved to be the most active catalysts in the complete oxidation of ethane in the temperature range 420–440°C. Stability studies showed that Mn oxide/SnO2 was very stable compared to Co oxide/SnO2 which lost activity on re-testing in similar reaction conditions. This loss in activity could be associated with Co oxide (as Co3O4) surface modification due to the operating temperature (200–500°C) and the presence of water formed during the reaction causing sintering, structural changes and valence state modification.

Complete Catalytic Oxidation of Methane and Ethane Over Supported Platinum, Palladium and Manganese Oxide Catalysts

Activities of Pt, Pd and Pt + Pd catalysts (metal concentrations ≤ 0.4%) supported on γ-A12O3 and on TiO2 (anatase) for the complete oxidation of methane (300 ppmv) in air have been measured as a function of temperature; values of T10, T50 and T90 together with the Arrhenius parameters (activation energy and pre-exponential factor) are reported. Pt is less active than Pd when on TiO2, but more active when on γ-Al2O3, contrary to literature reports, but on both supports the Pt + Pd mixture is much more active than either metal separately, T10 for Pt + Pd/γ-Al2O3 being as low as 228°C. Possible reasons for this are briefly considered.

Selective Adsorption and Catalysis on Aluminophosphate, MCM-41 Materials: Spectroscopy And Simulation

The selective adsorption of fluid mixtures in AlPO4–5, VPI-5 and MCM-41 have been determined using gas chromatography — mass spectrometry and molecular simulations. Qualitative agreement was obtained between experimental and calculated adsorption isotherms. The adsorbent materials were characterized using x-ray analysis and infrared FT spectroscopy. Synchrotron x-ray analysis provided an accurate lattice cell parameter for MCM-41 of 4.475 nm and was used to monitor changes in crystal structure on calcination. Strengths of intermolecular adsorbate-adsorbent interactions were obtained from differential scanning calorimetry. Rh complexes incorporated into these porous materials were found to exhibit selective alkene hydrogenation.