Showing papers by "John B. Moffat published in 1991"
TL;DR: In this article, the formation and decomposition of the 12-molybdophosphate and 12-tungstophosphates anions proceed through several species as the pH of the solution is changed, and no evidence was observed for the formation of the Keggin anion when solutions containing molybdate and either pyrophosphate or phosphite ions were studied.
76 citations
TL;DR: In this article, a series of 12-heteropoly oxometalate catalysts were studied to investigate the contribution of the cation in the IBA to methacrylic acid (MAA) reaction.
45 citations
TL;DR: In this paper, the effect of the ion exchange procedure on the pore structure and morphology of 12-heteropoly oxometalate salts was investigated and it was shown that the ion-exchanged salts possess microporous structures.
39 citations
TL;DR: Ion exchange of the ammonium, potassium, and cesium salts of 12-tungstophosphoric and 12-molybdophoric acids has been studied at 298 K as discussed by the authors.
36 citations
TL;DR: In this paper, a small quantity of tetrachloromethane (TCM) was added to the feedstream to enhance the selectivity of the feed stream to C2 and higher hydrocarbons.
Abstract: The oxidative coupling of methane has been tested over alkali- and alkaline earth-phosphate catalysts at 700 and 775 °C with and without the introduction of a small quantity of tetrachloromethane (TCM) to the feedstream. In general, the conversion of methane was enhanced by the addition of TCM but the effect on selectivity was dependent on the catalyst being examined. The selectivity to C2 and higher hydrocarbons and that to oxidation products have been shown to have a dependence on the cation radius/charge ratio.
20 citations
TL;DR: In this article, it was shown that the HPMo anions, Keggin Units (KU) are not decomposed upon addition of Cs up to 3 Cs per KU although modification of the surface dispersion of the HMPo seems to occur.
17 citations
TL;DR: In this article, the authors studied the cracking of C6-C8 alkenes on the ammonium salt of 12-tungstophosphoric acid (NH4PW ), showing that the cracking ability of the catalyst decreases rapidly with time on stream but attains a steady state after approximately three hours.
5 citations
TL;DR: At reaction temperatures of 300-350 °C isobutyronitrile and methacrylonitrile, in addition to the expected products of oxidative dehydrogenation, methacrylic acid, acetone, propene, CO and CO2, are produced from isobuyric acid passed over ammonium salts of 12-molybdophosphoric acid.
Abstract: At reaction temperatures of 300–350 °C isobutyronitrile and methacrylonitrile, in addition to the expected products of oxidative dehydrogenation, methacrylic acid, acetone, propene, CO and CO2, are produced from isobutyric acid passed over ammonium salts of 12-molybdophosphoric acid.
4 citations
TL;DR: In this article, the presence of a small quantity (less than 1 mole %) of tetrachloromethane in the feedstream promotes the oxidative coupling of methane over silica-supported oxide catalysts.
Abstract: The presence of a small quantity (less than 1 mole %) of tetrachloromethane in the feedstream promotes the oxidative coupling of methane over silica-supported oxide catalysts. The extent of this enhancement is found to be dependent both on the supported oxide as well as the alkali metal employed for solid phase doping purposes. The formation of an active chlorine species on the surface of the solid is suggested to alter its catalytic properties, which generates a new route, in addition to that occurring in the absence of chlorine species, for the coupling of methane.
4 citations
TL;DR: In this article, it was shown that the HPMo anions, Keggin Units (KU) are not decomposed upon addition of Cs up to 3 Cs per KU although modification of the surface dispersion of the HMPo seems to occur.
Abstract: The characterization by X-ray photoelectron spectroscopy (XPS), laser Raman spectroscopy (LRS), 31P NMR spectroscopy, and ion scattering spectroscopy (ISS) of cesium-doped silica-supported 12-molybdophosphoric acid (HPMo) is reported. The addition of cesium to a silica-supported 12-molybdophosphoric acid catalyst has been shown in previous work to poison the catalytic properties for partial oxidation of methane of the original HPMo catalyst. In this work it is shown that the HPMo anions, Keggin Units (KU) are not decomposed upon addition of Cs up to 3 Cs per KU although modification of the surface dispersion of the HPMo seems to occur. Evidence of a direct interaction between the KU and the cesium ions has been obtained from Raman, XPS, and ISS spectroscopies, resulting from an ion exchange between the proton of the acid and the Cs ions. XPS studies show that the Cs ions are well dispersed up to a loading corresponding to the exchange of the three H+ by 3 Cs+. In addition an electronic perturbation of Cs and Mo is detected by XPS as well as a shift of the main Raman band corresponding to a weakening of the MoOt, bond in accordance with the electronic effect of Cs deduced from the catalytic results.