Robert Rudham

Photocatalytic oxidation of propan-2-ol in the liquid phase by rutile

The photocatalytic oxidation of liquid propan-2-ol to acetone has been investigated using irradiated suspensions of pure rutile. It is shown that ultraviolet radiation, rutile and a source of oxygen are all necessary for measurable reaction to occur at 310 K. The parameters controlling the photoactivity of pure rutile, together with effects of adding hydrogen peroxide, water or dissolved salts to the reaction mixture, have been investigated. Supporting measurements with doped rutile and less pure anatase have also been made.The experimental results, which include values of the quantum yield, do not support a chain mechanism for acetone formation. Mechanisms are proposed, in which reactive species are formed by the surface trapping of both photoelectrons and photoholes.

Catalytic studies with dealuminated Y zeolite. Part 1.—Catalyst characterisation and the disproportionation of ethylbenzene

A series of highly crystalline, hydrothermally dealuminated Y zeolites has been prepared and further modified by extracting non-framework aluminium with Na2H2EDTA. The zeolites were comprehensively characterised using chemical analysis, X-ray diffraction, mid-infrared spectroscopy, 27Al magic-angle-spinning nuclear magnetic resonance (27Al MAS NMR), analysis of N2 adsorption isotherms and temperature-programmed desorption of NH3 to determined acid site concentrations. It is shown that aluminium from the framework resides in the micropores and freshly developed mesopores in a number of forms. Aluminium extraction with Na2H2EDTA increases both the pore volumes and the concentration of Bronsted acid sites, but leaves an average of five charge-balancing Al atoms per unit cell.Catalytic studies of ethylbenzene disportionation at 473 K show that Bronsted acid sites are the seat of an activity which increases following Na2H2EDTA extraction. There is evidence, however, for a synergistic interaction between Bronsted acid sites and extrastructural hydroxo-aluminium species in unextracted catalysts to yield sites of higher activity than in extracted catalysts. The reaction is believed to proceed by a dealkylation/alkylation mechanism which accounts for minor yields of ethene, which is held responsible for coke formation and catalyst deactivation.

Photo-oxidation of alcohols catalysed by platinised titanium dioxide

Abstract Irradiation of alcohols in benzene in the presence of platinised titanium dioxide provides a clean and convenient procedure for the synthesis of aldehydes and ketones on preparative scale.

Photocatalytic oxidation of propan-2-ol by semiconductor–zeolite composites

The photocatalytic oxidation of liquid propan-2-ol to propanone has been investigated using semiconductor–zeolite composites consisting of either CdS or TiO2 in Y zeolite. CdS-based composites were prepared by cation exchange with Cd2+ followed by sulfidation with either Na2S or H2S, whereas TiO2-based composite was prepared by Ti(OEt)4 impregnation followed by hydrolysis and calcination. Rate measurements at 303 K were made to assess how the activity of CdS-based material depended on reaction conditions; differences from CdS supported on γ-Al2O3 are ascribed to smaller CdS particles and the higher adsorption potential of the zeolite matrix for O2 and H2O. However, rate measurements under standard conditions over the temperature range 283–308 K yielded the same activation energies as for CdS and TiO2 supported on γ-Al2O3, 53 ± 2 kJ mol–1 for CdS-based catalysts and 21 ± 1 kJ mol–1 for TiO2-based catalysts. It follows that the physico-chemical properties of the semiconductor control the activation energy, whereas the zeolite matrix is responsible for controlling semiconductor particle size during preparation and modifying the effective reaction conditions through adsorption.

Infrared study of the interactions between NO and CO on Rh/Al2O3 catalysts

Infrared spectra of NO and NO + CO mixtures on Rh/Al2O3 are reported. At ambient temperatures NO alone was adsorbed non-dissociatively and gave no detectable reaction products. At T 413 K NO underwent partial decomposition to N2O(g) at surface sites which were rapidly poisoned as the reaction proceeded. The addition of NO to preadsorbed CO eliminated spectral bands characteristic of linear and bridged carbonyl species, but maxima due to gem-dicarbonyl species remained. The main products of the CO+NO reaction detectable by infrared spectroscopy were N2O(g), adsorbed isocyanate and CO2, either gaseous or chemisorbed. The extent of isocyanate formation depended on the relative amounts of NO and CO present, the gas-phase pressures of NO and CO and the order of addition of NO and CO to the Rh/Al2O3 catalyst. The order of addition did not affect the generation of N2O. The results are discussed in terms of reaction mechanism and types of catalytically active adsorption site. Dissociative adsorption of CO2 on Rh dispersed on alumina led to an adsorbed CO species giving an infrared band at 2015 cm–1.

Photocatalytic oxidation of liquid propan-2-ol by titanium dioxide

The photocatalytic oxidation of liquid propan-2-ol to propanone has been investigated using suspensions of TiO2 irradiated with filtered u.v. radiation at temperatures in the range 277–313 K. The dependence of reaction rate on the square root of the intensity of the incident radiation, together with low quantum yields, reflect the dominance of photoelectron and photohole recombination within the TiO2. The activation energy for reaction on pure rutile using 366 nm radiation, 27 kJ mol–1, was independent of reaction conditions. For pure anatase, five doped rutiles and coated anatase and rutile pigments, the activation energy under standardized conditions ranged from 31 to 91 kJ mol–1. These energies are considered to reflect the solid-state properties of the catalysts rather than the chemistry of propan-2-ol oxidation, which proceeds by a radical mechanism.

Photocatalytic dehydrogenation of liquid propan-2-ol by platinized anatase and other catalysts

The photocatalytic dehydrogenation of liquid propan-2-ol by suspensions of platinum and other metals supported on anatase has been investigated by following propanone formation under an N2 atmosphere. Measurements were made over the range 278–303 K using filtered 366 nm u.v. radiation.With Pt/TiO2 prepared by H2 reduction there was an appreciable dark reaction, which was absent with catalysts prepared by photodeposition. Reaction on photodeposited catalysts was consistently associated with an activation energy of 20 kJ mol–1, although the activity fell in the sequence Pt/TiO2 > Pd/TiO2 > Rh/TiO2 > Au/TiO2= 0 for catalysts with a metal content of 0.5 wt%. The activation energy is identical to that for photoreaction on the anatase support in the presence of O2 and is believed to be associated with the transport of photoelectrons through the anatase to either metal particles or adsorbed O2.

Photocatalytic dehydrogenation of liquid alcohols by platinized anatase

The photocatalytic dehydrogenation of liquid methanol, ethanol, propan-1-ol and propan-2-ol has been investigated using platinized anatase and 366 nm u.v. radiation over the range 278–303 K. Activities and activation energies for carbonyl-compound formation were effectively identical for the four alcohols on Pt(0.5)/TiO2 prepared by photodeposition. The activation energy of 20 kJ mol–1 is associated with photoelectron transport through the anatase to the Pt particles. With Pt(0.5)/TiO2 prepared by impregnation and H2reduction, identical activities for the four alcohols were achieved after O2 treatment. From the effect of u.v. intensity on the rate of propanone formation at 293 K, the limiting quantum yield was found to be 0.45 for photodeposited Pt(0.5)/TiO2 under N2 and 0.82 for support anatase under O2. Arrhenius plots for reaction at reduced u.v. intensities showed that the activation energy fell to zero when these quantum yields were achieved. Different mechanisms follow from the manner in which photoholes are surface trapped; two mechanisms for dehydrogenation with a limiting quantum yield of 0.5 are discussed.

Effects of preparation procedure on the surface properties of rhodium supported on γ-alumina

The decomposition of rhodium(III) nitrate, chloropentamminerhodium(III) chloride and rhodium(III) sulphite in atmospheres of hydrogen, nitrogen and nitrogen (80%)+ oxygen (20%) have been investigated by thermogravimetric analysis with the salts either pure or impregnated onto a γ-alumina support. The decomposition of rhodium(III) sulphite failed to give dispersions of rhodium metal on alumina but the reduction of the other salts to Rh0 was complete in nitrogen or hydrogen at temperatures between 400 and 690 K.Hydrogen and CO uptake data have shown that rhodium(III) nitrate led to a more finely divided dispersion of metal than did chloropentamminerhodium(III) chloride. Infrared spectra of CO absorbed on the Rh/Al2O3 dispersions were consistent with this conclusion. The effects of sintering and oxygen adsorption on the infrared spectra are reported. Linear and bridge-bonded CO were formed on exposed metal planes or two-dimensional rafts at Rh0 sites which were also active for the chemisorption of oxygen. Gem-dicarbonyl species were formed at monatomically dispersed rhodium sites or edge sites in rafts, both of which had cationic character through interaction with the alumina support. These sites were not active for the adsorption of oxygen.

Dehydration of propan-2-ol on X zeolites

The dehydration of propan-2-ol on moderately protonated X zeolites leads to the formation of both propene and di-isopropyl ether at temperatures in the range 383–430 K. Unexchanged zeolite was considerably less active, and only yielded propene at temperatures in the range 444–450 K. With protonated X zeolites the rates of formation of both products were investigated as a function of temperature, pressure of propan-2-ol and the extent of protonation, which lay between 8.6 and 28.4%. Decomposition at 411 K was completely poisoned by pyridine vapour. The Bronsted acidity of the accessible hydroxyl groups within the zeolites is considered to be the source of activity, and a mechanism involving carbonium and oxonium ions is proposed.