Ronald Pierantozzi

The mechanism of neopentane cracking over solid acids

Abstract Neopentane was used as a probe to test whether catalyst protons can attack the CC and/or the CH σ-bonds in the cracking of alkanes. Over a variety of solid acids approximately one CH 4 molecule was formed for every neopentane reacted. Moreover, in most cases nearly as much isobutene was formed. With HY zeolite (HY) and particularly with H-mordenite (HM), however, hydride transfer leading to paraffin formation became important or dominant. Generally, the results conformed to with the t -butyl ion either decomposing to isobutene or else undergoing secondary reactions. The latter tended to increase with the intensive factor of the acidity, i.e., with the strength of the acid-base interaction. The fraction of neopentane converted to CH 4 , when plotted in the Arrhenius fashion against T −1 , produced straight lines from which apparent activation energies could be calculated. Values obtained fell between 30 kcal/mol for silica-alumina and 14 kcal/mol for HM (the most acidic and active catalyst investigated). Controversial views found in current literature are discussed in light of the present results.

Support and cluster effects on synthesis gas conversion with supported ruthenium clusters

Abstract [Ru3(CO)12] and [H4Ru4(CO)12] supported on Al2O3 and MgO exhibited differences in catalytic behavior which can be attributed to the surface organometallic chemistry of the clusters. When supported on Al2O3, [Ru3(CO)12] decomposed to Ru metal on reaction with synthesis gas, and exhibited catalytic behavior that is similar to Ru/Al2O3 prepared by classical methods. On MgO, [Ru3(CO)12] resulted in significant CH3OH production from synthesis gas. After catalysis, the anionic cluster [Ru6C(CO)16]2− was identified on the catalyst, which results from the reaction of [HR3(CO)11]− and [Ru6(CO)18]2−, originally present on the support, with CO + H2. [H4Ru4-(CO)12] supported on Al2O3 and MgO also resulted in significant oxygenate yields from CO + H2. [H3Ru4(CO)12]− was originally present on the surface and reacts with synthesis gas to give [Ru6C(CO)16]2−. The oxygenate selectivity is suggested to be a result of the presence of intact metal clusters on the surface.

Si diffusion coating on steels by SiH 4 /H 2 treatment for high temperature oxidation protection

The reaction of SiH{sub 4}/H{sub 2} mixtures with iron and steels was studied at a total pressure of 1 atm and temperatures above 500 {degree}C. When the amount of water vapor in the gas mixture is carefully controlled, a metal silicide diffusion coating forms at low temperatures (below 900 {degree}C). Composition and structure of the Si diffusion coatings were determined with Auger depth profiling and x-ray diffraction. Kinetics of the surface reaction between SiH{sub 4} and the metal substrate as well as the behavior of these films in severe environments at high temperatures were studied by a microgravimetric technique. Characterization of these Si coatings on iron, low carbon steel (1010), 9% Cr/1% Mo steel (alloy A182F9), and stainless steels (310) and their applications to reduce oxidation, nitriding, or coking at high temperatures or corrosion in mineral acids are described.

Synthesis of oxygenates from CO and hydrogen over supported metal clusters

Metal clusters serve as precursors to highly dispersed or unique supported metal catalysts. While numerous studies describe the preparation and characterization of cluster derived catalysts, only a few describe their use for selective synthesis gas reactions. For these reactions, the product type (i.e., oxygenates or hydrocarbons) is generally similar to that produced on conventionally prepared catalysts. The authors reports here studies on supported metal cluster derived catalysts for CO hydrogenation that illustrate the differences between cluster precursors and conventional precursors. The author shows that cluster precursors can result in product types that are different than those produced by conventional catalyst preparations. The paper also shows that the choice of cluster and support is critical in determining the product distribution. Two types of catalyst systems were studied: an anionic metal cluster based on Fe and Mn impregnated on MgO, Al/sub 2/O/sub 3/, or ZrO/sub 2//Al/sub 2/O/sub 3/; and Ru carbonyl clusters on TiO/sub 2/. 12 references.