Showing papers by "John B. Moffat published in 1989"
TL;DR: In this paper, nonporous heteropoly oxometalates are shown to be capable of absorbing polar molecules into their bulk structures while retaining their properties as solids, and the results from photoacoustic FTIR, X-ray diffraction and sorption measurements are employed to illustrate this feature.
71 citations
TL;DR: In this article, it was shown that a small amount of dichloro- or tetrachloromethane is added to the feed stream in the conversion of methane on silica-supported 12-tungstophosphoric acid produces substantial changes in conversion, selectivity, and rates of consumption of reactants and formation of products.
28 citations
TL;DR: The introduction of carbon tetrachloride to the feed stream in the conversion of methane to C2 hydrocarbons over a variety of silica-supported oxides is shown to alter both the conversion and selectivity.
Abstract: The introduction of carbon tetrachloride to the feed stream in the conversion of methane to C2 hydrocarbons over a variety of silica-supported oxides is shown to alter both the conversion and selectivity, but, notably with oxides of Ba, Cs and Mn produces remarkable increases in the yield and selectivity to C2H4 and C2H6, particularly the former.
26 citations
TL;DR: In this paper, three effects on the properties of the supported 12-molybdophophosphoric acid catalyst due to the addition of cations have been discerned, one is attributed to the removal of protons by substitution, leading to the blocking of the oxygen extraction step which generates vacancies in the Keggin structure.
24 citations
TL;DR: In this article, the alkylation of toluene with methanol has been studied on two microporous heteropoly oxometalates, the ammonium salts of 12-tungstophosphoric and 12-tenantosilicic acids.
20 citations
TL;DR: In this paper, the conversion of methylethylbenzenes, and in particular 1-methyl-2-ethylbenzene, has been studied on two microporous heteropoly oxometalates.
18 citations
TL;DR: In this paper, the catalytic properties of microporous and nonporous heteropoly oxometalates and ZSM-5 zeolites prepared in the absence of an organic templating agent have been studied in the cracking of n-hexane at 648, 673 and 698 K.
18 citations
TL;DR: In this article, the effect of residence times and of temperatures on conversion, selectivity and rates of methane was examined over silica supported thallium oxide catalysts in the temperature range 657-825°C.
16 citations
TL;DR: In this paper, the results from cation exchange and the addition of a chloro-additive are interpreted and a mechanism with common features is proposed for the methanol and methane conversion processes.
Abstract: Heteropoly oxometallates have been employed in the heterogeneous catalysis of the conversion of methanol to hydrocarbons and the partial oxidation of methane. In the former process methanol is first protonated at Bronsted-acid sites, but at higher temperatures the heteropoly anions are partially methylated subsequent to scission of the C—O bonds in protonated methanol. With silica-supported 12-molybdophosphoric acid the exchange of the protons by cations effectively poisons the catalyst for the conversion of methane. Introduction of a chloro-additive to the feedstream in the latter process produces changes in the conversion and selectivity which are markedly different for the molybdenum- and tungsten-containing catalysts. With the former the conversion of methane is increased while the selectivity to partial oxidation products is decreased. With the latter the former comments are also applicable but selectivities to methyl chloride reach as high as 90 mol %. The results from cation exchange and the addition of a chloro-additive are interpreted and a mechanism with common features is proposed for the methanol and methane conversion processes.
13 citations
TL;DR: In this paper, the alkylation of toluene with methanol has been studied on two microporous heteropoly oxometalates, the ammonium salts of 12-tungstophosphoric and 12-tenantosilicic acids.
Abstract: The alkylation of toluene with methanol has been studied on two microporous heteropoly oxometalates, the ammonium salts of 12-tungstophosphoric and 12-tungstosilicic acids. Alkylation of the benzene ring to produce xylenes and the trimethyl- and tetramethylbenzenes was found to be the predominant process. Evidence is presented for an alkylation mechanism involving the methylation of the anions of the catalysts. Compositions of the xylene isomers in the product suggest the presence of a shape-selective factor.
1 citations