William Lewis Henderson Watkins

Incorporation of La3+ into a Pt/CeO2/Al2O3 catalyst

The effects of La3+ incorporation into a Pt/CeO2/Al2O3 catalyst were investigated by a combination of activity, temperature-programmed reduction (TPR), oxygen storage capacity (OSC), noble-metal surface area, and X-ray diffraction (XRD) measurements. Incorporation of La3+ ions into the Al2O3, before CeO2 is added, promoted higher Pt and CeO2 dispersions. The oxygen storage capacity was also higher in the presence of La3+. This is attributed to a combination of Pt and CeO2 particle-size effects and possible blockage of the reaction between Al2O3 and CeO2. The XRD data show that La3+ forms LaAlO3 with Al2O3 and prevents α-Al2O3 formation after various heat treatments.

Incorporation of La3+ into a Rh/γ-Al2O3 catalyst

The effects of La[sup 3+] incorporation into Rh/[gamma]-Al[sub 2]O[sub 3] were investigated by a combination of temperature-programmed reduction, X-ray photoelectron spectroscopy, CO chemisorption, and reactivity measurements. The reduction of Rh[sup 3+] following high-temperature (> 600 C) oxidation was more facile and the dispersion of Rh was higher with La[sup 3+] present. Notwithstanding, the catalytic activity, as manifested by the HC[sub 2]CO[sub 3] and NO[sub x] conversion efficiencies, was lower in the presence of La[sup 3+]. This is attributed to a combination of Rh particle-size effects and possible La-Rh compound formation under oxidizing conditions. Changes brought about by high-temperature oxidation in catalysts both with and without La[sup 3+] were completely reversed by high-temperature reduction.

Characterization of silver catalysts for the oxidation of methanol

Abstract The selection of a silver catalyst system for further study was determined on a basis of cost and its ability to oxidize formaldehyde selectively. In addition a silver catalyst can provide a low light off temperature for the conversion of methanol to carbon dioxide and water vapor. Silver catalysts were prepared by the deposition of solutions of silver nitrate or silver chloride on gamma alumina washcoat supported on cordierite monolith. These silver catalysts were characterized by a variety of analytical techniques including TEM, SEM, EMP, STEM, XRF, XRD and FTIR. It is concluded that the best silver catalyst is prepared by deposition of silver from a solution of silver ammnonium chloride onto a cordierite supported high surface area gamma alumina washcoat, drying at 100°C in air, followed by reduction in flowing 3% H2 in N2 at 500°C for 4 h. This procedure will produce a silver catalyst with highest activity, largest retention and most uniform distribution of silver. The procedure also retains the concentration of silver and the gamma phase of alumina at temperatures as high as 1000°C in air for as long as 6 h. Due to the inability of normal TEM imaqing modes to obtain silver particle size information in the presence of the small gamma alumina washcoat particles a model system was made to test the ability of a dedicated STEM to furnish that information. The model system consisted of silver particles in the range of 1 to 50 nm which had been evaporated onto a uniform thin film of alumina. High resolution X-ray maps obtained from the model system demonstrate the ability to determine location and size of silver particles > 5 nm. A number of catalysts containing noble and base metals supported on gamma alumina washcoat on a cordierite monolith have also been studied. Laboratory flow reactor studies and chassis dynamometer studies using a Mercury Lynx modified to burn neat methanol have shown the following order of activity for conversion of methanol burned in experimental or engine exhaust gas: Pd > Ag > Pt + Rh > CuO + ZnO + Cr2O3 > Ni.

Characterization of Automotive Catalysts Exposed to the Fuel Additive MMT

A series of in-use catalysts having mileage of 22,000 to 43,000 miles was characterized to determine the effect of the fuel additive MMT. The analytical techniques included visual examination, x-ray fluorescence, x-ray diffraction, optical microscopy, scanning electron microscopy, and electron microprobe. In addition, catalyst activity was measured and compared to the catalyst activity from a pulsator aged catalyst without the MMT additive in the feed gas composition. Characterization results show a significantly thick layer (5-20 microns) covering the surface of the catalysts which results in the increase of mass transfer resistance. Steady state R and light-off measurements indicated catalyst efficiency is also significantly reduced as exposure to MMT is increased.

Sulfur-poisoning of the oxidation of H2 and CO over A (Pd+CeO2)γ-A1203 catalyst

Abstract The effect of SO 2 on the activity of a (Pd+CeO 2 )γ-A1 2 0 3 catalyst was evaluatedwith respect to the oxidation of H 2 and CO by 0 2 . The presence of SO 2 at a concent-ration of 20 ppm adversely affected the catalyst activity in varying degrees. Inthe case of H 2 oxidation, the extent of poisoning increased with the H 2 /0 2 ratioand the overall reaction was found to be of negative order (-0.5 or 1 depending on temperature) with respect to H 2 and of second order with respect to 0 2 . The H 2 oxidation was also significantly inhibited by CO. In the case of CO oxidation in the absence of H 2 , the S-poisoning was found to be relatively moderate and the overall reaction was of 1/2 order with respect to both CO and 0 2 . The S-poisoning of CO oxidation was enhanced by the presence of H 2 , especially when the oxygen present was below the stoichiometric amount.

Stabilization of rhodium/alumina catalysts by silicon exchange

Abstract Modification of alumina by exchange of surface hydroxyl groups with tetraethyl orthosilicate was investigated as a method for preventing interactions between rhodium and alumina in high-temperature (1173 K) oxidizing environments. Temperature-programmed reduction experiments, together with catalytic reactivity measurements and BET surface area measurements were used to characterize both the silicon exchanged rhodium/alumina catalyst and reference catalysts comprised of rhodium/alumina (without silicon) and rhodium/zirconia admixed with blank alumina. Relative to the reference catalysts, the silicon exchanged catalyst showed less interaction between the Rh and alumina and better retention of BET surface area after high temperature steam-oxygen aging. The data suggest that dehydroxylation of alumina at elevated temperatures is an important factor in the interaction between rhodium and alumina. Exchange of surface hydroxyl groups with tetraethyl orthosilicate appears to stabilize those surface sites where rhodium and alumina would otherwise interact. On the other hand, silicon exchange results in a weaker interaction between Rh and the support and growth of larger Rh particles than obtained on the unmodified alumina.