Ayman Hammoudeh

PRETREATMENT EFFECTS ON THE CATALYTIC ACTIVITY OF JORDANIAN BENTONITE

De-tert-butylation of 2-tert-butylphenol was carried out over thermally-treated and acid-treated Jordanian bentonite clay samples. This reaction was found to follow first-order kinetics for all clay samples with different pretreatment procedures. The apparent rate constant, k, was also determined, and found to depend on the pretreatment. Thermal pretreatment at temperatures up to 250°C has an enhancing effect on surface acid sites. The total surface acidity (Ho <4.8) and the concentration of strong acid sites peaked at 250°C. Also, as a result, the maximum catalyst activity was obtained with samples treated at this temperature. Acid pretreatment with 0.10 M HCl, 1.0 M H2SO4 or 1.0 M H3PO4, followed by thermal treatment at 250°C produced the best enhancement effect on the surface acidity and catalytic activity.

Selective Hydrogenation of Cinnamaldehyde Catalyzed by Ruthenium (II) Complexes Based on Azoimine Ligands

In this work, four Ru (II) complexes based on azoimine ligands were tested with respect to their catalytic behavior in the liquid phase hydrogenation of cinnamaldehyde. The introduction of a thiophenyl substitution in the azoimine ligand was found to enhance significantly the catalytic activity and selectivity of the Ru complex. The catalytic behavior of the most active complex in this work was studied with respect to the effect of the co-catalyst KOH, the Ru complex and the cinnamaldehyde (CALD) concentrations as well as with respect to the effect of the reaction temperature. KOH is needed to transform the Ru complex into a reactive form and the higher the KOH concentration in the system, the higher is the efficiency of the catalytic system. The order of this activation process with respect to KOH and with respect to the Ru complex was found to be one in both cases. With a CALD-to-Ru ratio of 84:1 at T=86 o C, pH2=4 bar and [KOH]= 5.82×10 -3 M, a complete conversion could be accomplished in only 90 minutes with selectivity to cinnamyl alcohol approaching 95%. Increasing the initial concentration of cinnamaldehyde has, under the reaction conditions investigated in this work, a negative effect on the rate of hydrogenation with an order decreasing with increased concentration from -1 to -3. Based on our results, an outer-sphere mechanism is ruled out to operate in this system.

Hydrocatalytic Reduction of Nitrate in Aqueous Solution over Titania Supported Pd-Au Catalysts

Some Pd and/or Au containing catalysts supported on TiO2 were prepared by impregnation (I) and incipient witness (IW) methods. These catalysts that include Au3%/TiO2-I, Au1.5%/TiO2-I, Au1.5%Pd1.5%/TiO2-I, Pd1.5%/TiO2-I, Pd3%/TiO2-I and Au6.0%Pd0.2%/TiO2/IW were characterized by means of XRD. The supported metal was thereby determined to have a particle size around 50 nm. All catalysts were tested in the reduction of nitrate ions in aqueous solution and in the presence of hydrogen gas. All tested catalysts were found to be of relatively high activity and with high dinitrogen selectivity in this respect. Pd-Au/TiO2 catalysts were found to have high selectivity but slightly lower activity than Pd-catalysts. Incorporation of Au into Pd catalysts has improved their selectivity. Au1.5%Pd1.5%/TiO2-I produces less nitrite than Pd3%/TiO2I, indicating that alloying has positive effects on the reduction of nitrate. The alloying effects were much more pronounced in the case of Au6%Pd0.2%/TiO2/IW where more than 87% nitrate conversion was achieved with ~100% dinitrogen selectivity in 30 min. of reaction and without any detectable nitrogen fixation.