Jule Anthony Rabo

Reactions of carbon monoxide and hydrogen on Co, Ni, Ru, and Pd metals

The adsorption of CO on Ni at 300 °C is dissociative, resulting in disproportionation to CO2 and a NiC species. The surface carbon species formed from CO is readily hydrogenated at 300 °C to methane. At room temperature, the CO sorption on Ni is nondissociative, and the adsorbed CO is inert to H2. In contrast, the NiC species formed from CO at 200 to 300 °C reacts with H2, even at room temperature, forming C1 to C4 paraffins. Co and Ru metals show behavior very similar to that of Ni. In contrast to Ni, Co, and Ru metals, the adsorption of CO on Pd at 300 °C is nondissociative, and the chemisorbed CO is less reactive to H2 than the MC species formed on Ni, Co, or Ru.

Selective formation of methanol from synthesis gas over palladium catalysts

Abstract Hydrogenation of carbon monoxide over supported Pd catalysts gave methanol in high selectivity at 260–350 °C and 150–16,000 psig of pressure. Methanation became significant only outside the temperature-pressure regime for which methanol formation is thermodynamically favorable. The behavior of Pt and Ir appears similar although fewer data have been gathered. The catalytic behavior of these three noble metals toward synthesis gas is thus not only different from that commonly thought but also sharply contrasted with that of the other Group VIII metals for which ultimate CO bond hydrogenolysis and hydrocarbon formation are a dominating feature. Silica-supported Pd was directly compared with Ni at 314 °C and 12.25 atm of CO:H2 (30:70); Pd not only gave methanol formation rather than the methanation observed for Ni but also much less chain growth activity than Ni. It is suggested that these differences in catalytic performance may be related to the inability of Pd (and Pt and Ir as well) to chemisorb CO dissociatively at reaction temperatures, compared to other Group VIII metals.

Acid Function in Zeolites: Recent Progress

The purpose of this paper is to review the chemical and structural characteristics of zeolites deemed relevant to acidity and to acid catalysis. Several tentative conclusions are also drawn, in order to interpret some of the important chemical phenomena. In view of the availability of several detailed reviews on catalytic data, these will not be reviewed here.

Heterogeneously catalyzed vapor-phase oxidation of ethylene to acetaldehyde

Abstract A heterogeneous catalyst system has been developed for the vapor-phase oxidation of ethylene to acetaldehyde. The catalyst consists of palladium-doped vanadium pentoxide and, usually, a third component such as Ti, Ru, Pt, or Ir. Mechanistic studies, especially by ESR spectroscopy, have established a redox mechanism with the palladium ions playing a central role. The catalyst system operates under mild conditions (110–175 °C and 1–30 atm) with good efficiency and high space-time yields.

Catalytic cracking studies and characterization of steamed Y and LZ-210 zeolites

Abstract Catalytic cracking catalysts prepared using Y zeolite crystals which have been silicon enriched by treatment with ammonium fluorosilicate solution show substantially superior crystal retention upon exposure to severe hydrothermal treatments, relative to similarly treated Y-zeolite-based catalysts. The silicon-enriched Y-based catalysts, following hydrothermal pretreatment, also show superior activity retention and higher gasoline selectivity relative to Y-zeolite-based catalysts. The study of steamed Y and the silicon-enriched Y product by solid-state MAS NMR shows that upon steaming the silicon-enriched zeolite displays superior retention of the framework structure relative to Y, and that the Y product shows not only aluminum loss but also significant silicon loss from the crystal framework, contributing to deterioration of the crystal. Thermometric titrations of Y zeolites, following exposure to steam treatments of increasing severity, indicates that upon severe steam treatment the strong acid character typical of stabilized Y is greatly reduced while a substantial concentration of milder acid sites is formed, similar in acid strength to amorphous silica-alumina gel. These data are interpreted on the basis that upon steaming amorphous alumina and silica-alumina phases are formed, occluded in the zeolite crystal, and that the occluded amorphous, acidic debris adversely affects cracking selectivity to produce gasoline.

Skeletal Rearrangement Reactions of Olefins, Paraffins and Aromatics Over Aluminophosphate Based Molecular Sieve Catalysts

Medium pore aluminophosphate based molecular sieves with the -11, -31 and -41 crystal structures are active and selective catalysts for 1-hexene isomerization, hexane dehydrocyclization and C8 aromatic reactions. With olefin feeds, they promote isomerization with little loss to competing hydride transfer and cracking reactions. With C8 aromatics, they effectively catalyze xylene isomerization and ethylbenzene disproportionation at very low xylene loss. As acid components in bifunctional catalysts, they are selective for paraffin and cycloparaffin isomerization with low cracking activity. In these reactions the medium pore aluminophosphate based sieves are generally less active but significantly more selective than the medium pore zeolites. Similarity with medium pore zeolites is displayed by an outstanding resistance to coke induced deactivation and by a variety of shape selective actions in catalysis. The excellent selectivities observed with medium pore aluminophosphate based sieves is attributed to a unique combination of mild acidity and shape selectivity. Selectivity is also enhanced by the presence of transition metal framework constituents such as cobalt and manganese which may exert a chemical influence on reaction intermediates.

Molecular Sieve Effects in Carboniogenic Reactions Catalyzed by Silicoaluminophosphate Molecular Sieves

Several novel silicoaluminophosphate (SAPO) molecular sieves representing a broad variety of crystal structures and pore sizes ranging from small to large were evaluated for catalytic activity in the reactions of propylene oligomerization and toluene methylation. The medium pore SAPOs −11, −31, −40 and −41, combining features of unique pore structure and mild acidity were outstanding catalysts with high selectivity to gasoline range olefinic products in propylene reactions and high para xylene yields in toluene methylation.

The Reaction of Surface Carbon with Water on Ni and Co Catalysts; A New Process for the Production of Concentrated Methane from Dilute Carbon Monoxide Waste Streams

The sorption of CO on supported Co, Ni and Ru is substantially dissociative leading to CO disproportionation, forming CO 2 and a carbon species attached to the metal surface. This carbon species reacts with H 2 instantaneously at 300°C forming methane. The carbon species also reacts readily with water to form equimolar CO 2 + CH 4 . The high efficiencies of CO disproportionation and the formation of methane from the carbon species and water led to the development of a new process combining these two reactions into a reaction cycle using a single catalyst bed.

New Directions in Molecular Sieve Science and Technology

Progress in molecular sieve science and technology is reviewed in the fields of synthesis, catalyst characterization, and catalysis. In synthesis, the molecular sieve crystal types and compositions have been greatly expanded from zeolites and pure silica materials to aluminophosphate-based molecular sieves representing more than two dozen crystal structures and many more chemical compositions, with up to six framework metals chosen from 13 elements. These new molecular sieves represent a variety of chemical properties, and they display weak to medium-strong acid catalytic activity.

International Symposium on Catalysis by Microporous Materials

Publisher Summary This chapter reviews catalysis by microporous materials. Improvements in process economics are discussed. Process economics needs improvements both on the process side and in the performance of the catalysts. Both aims are best satisfied by increasing conversions and selectivities and by reducing the number of process steps. These improvements tend to minimize the amounts of capital, raw materials, and energy needed. Catalysts are needed to realize the great industrial opportunities offered by superacid-type activation of several chemically inert, cheap raw materials. Uniform active sites on the catalyst, easy chemical and thermal manipulation of the active sites, and multifunctionality are helpful to minimize process steps by combining several chemical transformations over the same catalyst bed.