Kazushi Arata

Preparation of superacids by metal oxides for reactions of butanes and pentanes

Recent works on preparation of solid superacid catalysts which are active for reactions of butanes and pentanes are reviewed. Sulfated metal oxides are obtained by adsorbing sulfate ion onto amorphous oxides of Fe, Ti, Zr, Hf, Sn, and Si followed by calcination in air; a superacid of Al2O3 is prepared from the crystallized oxide. Superacids by metal oxides are synthesized in the same manner as those of the sulfate superacids by supporting ZrO2, SnO2, TiO2, and Fe2O3 with WO3 and ZrO2 with MoO3 and B2O3. Metal-promoted superacids which are highly active for the reaction of butane to isobutane are prepared by addition of salts of Pt, Ir, Rh, Ru, Os, Pd, Fe, and Mn (equivalent to Pt of 7.5 wt%) to sulfated zirconia gel followed by calcination. Similarly active catalysts are obtained by treatment of zirconia-supported Fe2O3 with sulfuric acid and calcination for long period.

Synthesis of solid superacid catalyst with acid strength of H0⩽–16.04

A solid superacid catalyst with an acid strength of H0⩽–16·04, which was active for reactions of propane and butane, was obtained by exposing Zr(OH)4, prepared by the hydrolyses of ZrOCl2 and ZrO(NO3)2, to 1 N H2SO4 and then calcining in air at 575–650 °C.

Solid catalyst treated with anion: XVIII. Benzoylation of toluene with benzoyl chloride and benzoic anhydride catalysed by solid superacid of sulfate-supported alumina

Abstract A solid superacid catalyst with an acid strength of −16.04≫Ho⩽ −14.52 was obtained by exposing γ-Al2O3 to 2.5 M H2SO4 followed by calcining in air at 550–650°C. The catalyst was active for the benzoylation of toluene with benzoyl chloride or benzoic anhydride in a heterogeneous system. Specific surface area of the catalyst was much smaller than that of the oxide which had not undergone the sulfate treatment. X-ray photoelectron spectroscopy (XPS) showed the catalyst surface to be composed of SO2−4 and Al2O3. It is suggested that the benzoylation was performed on Bronsted sites created by adsorption of water on Lewis sites of the catalyst.

Synthesis of highly active superacids of SO4/ZrO2 with Ir, Pt, Rh, Ru, Os, and Pd substances for reaction of butane

Highly acidic catalysts stronger than the SO4/ZrO2 superacid with an acid strength of Ho ⩽ −16.04 were obtained by kneading Zr(OH)4 with ammonium sulfate together with chlorides of Ir, Pt, Rh, Ru, Os, and Pd followed by calcining in air at 600°C, the metal concentration being equivalent to Pt of 7.5 wt% based on the hydroxide. The catalysts with Ir and Pt materials were highest in activity for the skeletal isomerization of butane to isobutane. The present catalysts were not obtained by treating the crystallized oxide, ZrO2 calcined at 700°C, but the amorphous form followed by calcination to the crystallization.

Skeletal isomerization mechanism of alkanes over solid superacid of sulfated zirconia

Abstract Skeletal isomerizations of n-butane and n-pentane were performed over solid superacids of sulfated zirconia and Pt-promoted sulfated zirconia. Changes in apparent activation energy and product selectivity were observed during the reactions. Isomerization proceeded by a monomolecular mechanism on Lewis acid sites in the initial period; then it changed to a bimolecular mechanism on Bronsted acid sites by forming surface alkenes. By addition of hydrocarbons or hydrogen, the monomolecular reaction became predominant. n-Pentane was converted into isopentane with very high selectivity. The overall mechanism of acid-catalyzed skeletal isomerization of alkanes is discussed.

Synthesis of solid superacid of tungsten oxide supported on zirconia and its catalytic action for reactions of butane and pentane

A solid superacid catalyst with an acid strength of H0⩽–14.52 was obtained by impregnating Zr(OH)4 or amorphous ZrO2 with aqueous ammonium metatungstate followed by calcining in air at 800–850 °C (13 wt.% W); this catalyst was active for the isomerisations butane to isobutane at 50 °C, and pentane to isopentane at 30 °C.

Organic syntheses catalyzed by superacidic metal oxides: sulfated zirconia and related compounds

Recent studies on organic syntheses catalyzed by solid superacids, which are sulfate-supported metal oxides and tungsten- or molybdenum-supported metal oxides, are reviewed. The synthetic reactions are Friedel–Crafts acylations, reactions between amines and ketones, esterifications of acids with alcohols, and others. The catalysts are satisfactorily active in a heterogeneous liquid–solid system, recoverable, and reusable, and they offer new opportunities for developing environmentally benign and friendly processes in organic syntheses.

Solid catalyst treated with anion: XIX. Synthesis of the solid superacid catalyst of tin oxide treated with sulfate ion

Abstract A solid superacid catalyst with an acid strength of Ho ⩽ −16.04 was synthesized from tin hydroxide, which was obtained from the solution of pH 10, by exposing to 3 M H 2 SO 4 followed by calcination in air at 823 K; the catalyst, SO 2- 4 /SnO 2 , was active for the skeletal isomerization of butane to isobutane at room temperature. The specific surface area of SO 2- 4 /SnO 2 was much larger than that of SnO 2 without the sulfate treatment; by X-ray diffraction (XRD) analysis the degree of crystallization of the former material was much lower than that of the latter. Infrared (IR) spectra showed the catalyst to possess a bidentate sulfate ion coordinated to the metal. The present superacid showed the catalytic action of oxidation at elevated temperatures of >450 K; acetaldehyde and acetone were obtained as products from the hydration of ethene, and high selectivity of >95% for the formation of cyclohexanone from cyclohexanol was observed in the presence of water.

Friedel-Crafts reaction in the heterogeneous system: V. Friedel-Crafts benzylation and benzoylation of toluene catalyzed by calcined iron sulfates

The Friedel-Crafts benzylation of toluene with benzyl chloride was carried out at 45 °C over ferrous and ferric sulfates calcined in air at 700, 800, and 900 °C. The benzoylation of toluene with benzoyl chloride was also performed at 110 °C over both iron sulfates heat-treated at 500, 700, 900 °C. The catalysts prepared by calcining both sulfates at 700 °C showed the maximum activity in both reactions. The products were 41% ortho-, 7% meta-, and 52% para-benzyltoluene for the benzylation and 18–22% ortho-, 2–4% meta-, and 74–78% para-methylbenzo-phenone for the benzoylation in all the analyzed runs. The ratio of rate of the benzoylation in toluene and benzene, kTkB, was 7.4 and 6.3 for FeSO4 and Fe2(SO4)3 calcined at 700 °C, respectively, which are surprisingly small compared with that for AlCl3 (ktkb = 110–115). From the former values, the positional selectivities of toluene, of, mf, pf, were obtained as 3–5, 4–9, and 32, respectively. The specific surface areas of calcined sulfates were 49–71 m2/g, indicating no relationship between them and the catalytic activities. The analysis of Fe and S contents of the catalysts showed that both ferrous and ferric sulfates are mainly remained as sulfate forms at 500 °C of calcination and decomposed to form iron oxides containing 0.15% S at 700 °C. Mossbauer spectra showed that ferrous sulfate calcined in air consists of 73% Fe2+ and 27% Fe3+ at 300 °C and 100% Fe3+ above 500 °C. On the basis of the observed results, the nature of active sites of catalyst was discussed.

Determination of acid strength of solid superacids by temperature programmed desorption using pyridine

Acid strength of solid superacids was determined by temperature programmed desorption using pyridine. An approximately linear relationship exists between the acid strengths of solid acids determined by the Hammett method and the termination temperature of pyridine desorption. The acid strength of colored superacids versus temperature relationships practically fell on the linear line.