Francis M. Mulcahy

The adsorption of metal oxyanions on alumina

The adsorption of perrhenate, permanganate, molybdate, tungstate, and chromate on alumina was studied at pH 4.5. The effect of nitrate in the impregnation solution on the adsorption of these ions was examined as well as the effect of washing the freshly prepared catalysts. The uptake of perrhenate and permanganate decreased with increasing nitrate in the impregnation solution; the uptake of molybdate, tungstate, and chromate was unaffected. Washing the catalysts almost completely removed perrhenate, permanganate, and chromate, but allowed a significant amount of molybdate and tungstate to remain on the alumina. It is concluded that tungstate and molybdate adsorb on two types of surface sites, producing loosely and tightly bound surface species. From the amounts of molybdate and tungstate adsorbed, and from EXAFS results from washed and unwashed Mo/Al2O3 samples, both loosely and tightly bound molybdate and tungstate are polymeric in nature. The results are discussed in terms of electrostatic and surface reaction models.

The effect of the isoelectric point on the adsorption of molybdates on fluoride-modified aluminas

Abstract The isoelectric point (IEP) of γ-alumina was modified by the addition of various amounts of fluoride. The modified aluminas were used as supports for molybdenum catalysts prepared by equilibrium adsorption at pH = 6.5. Also, the adsorption of molybdate on supports containing various amounts of fluoride was studied as a function of pH. The amount of molybdenum adsorbed on the fluoride-modified aluminas was found to decrease as the IEP of the carrier decreased. An electrostatic model is used to interpret the results.

Catalytic Hydrogenation of L-Ascorbic Acid (Vitamin C): A Stereoselective Process for the Production of L-Gulono-1, 4-Lactone

Abstract Reduction of functional groups with hydrogen gas is one of the most important reactions in organic chemistry, dating to the first hydrogenation of ethene to ethane reported by Von Wilde in 18741. Indeed, alkenes are generally rapidly hydrogenated, in the presence of a catalyst, usually, platinum, Raney nickel, palladium, or rhodium on carbon, to the corresponding alkane via heterogeneous reaction. Most undergraduate, introductory texts introduce this reaction as occurring via a stermspecific syn addition, although this is an oversimplification, due to possible rearrangements on the catalyst surface2. While the chemistry of Vitamin C (L-ascorbic acid), in regards to oxidative degradation, is well studied, its behavior under reductive conditions has been relatively overlooked. The catalytic reduction of ascorbic acid has been reported earlier (24 hours, palladium catalyst, water, 50°) by workers at Pfizer3.

Surface coverage of rhenium-alumina catalysts

The surface coverage of a series of rhenium-alumina catalysts prepared by equilibrium adsorption was determined by ion scattering spectroscopy (ISS) and infrared spectroscopy (IR). The coverage results were compared with those determined from previously published CO 2 chemisorption data. The ISS results show an almost linear increase in Re coverage with increasing Re loading, reaching ∼30% coverage for a loading of ∼6.5 wt.% Re. The near-linearity of the coverage with increasing Re content indicates a uniform build-up of the surface species. The Re cross-sections calculated from the corresponding surface coverages (24.8-30.5 A 2 /Re) were comparable with those previously reported for the Re/Al 2 O 3 system. The surface coverage determined from IR was shown to depend on the extent of dehydroxylation of the samples. Following pretreatment at 500°C, the coverage values for high loading catalysts were comparable with those obtained from ISS. However, the IR method yielded increasingly higher coverage values with decreasing Re loading. The Re cross-section values estimated from the corresponding surface coverages indicate an increased overestimation of the coverage with decreasing loading. As expected, the CO 2 chemisorption method consistently leads to an overestimation of the Re surface coverage.