Justin S. J. Hargreaves

Metal Oxide Catalysis

With its two-volume structure, this handbook and ready reference allows for comprehensive coverage of both characterization and applications, while uniform editing throughout ensures that the structure remains consistent. The result is an up-to-date review of metal oxides in catalysis. The first volume covers a range of techniques that are used to characterize oxides, with each chapter written by an expert in the field. Volume 2 goes on to cover the use of metal oxides in catalytic reactions. For all chemists and engineers working in the field of heterogeneous catalysis.

Catalytic synthesis of methanol and formaldehyde by partial oxidation of methane

Abstract The recent literature concerning the partial oxidation of methane to methanol and formaldehyde is reviewed, with particular attention to advances made since 1985. A number of topics are discussed in detail including approaches that can be taken in ranking catalyst performance as well as the extensive literature concerning simple oxide and supported oxide catalysts. It is considered that novel experimental approaches are required if high selectivity of commercial significance is to be achieved. Against this background the design methods for novel materials and alternative experimental approaches are highlighted.

Waste materials – catalytic opportunities: an overview of the application of large scale waste materials as resources for catalytic applications

In this overview, we present examples of the use of high volume waste materials in catalysis or for catalyst synthesis. Waste materials derived from both industrial and biological sources have attracted interest and this is briefly summarized. The materials described include red mud, aluminium dross, fly ash, blast furnace slag, rice husk and various kinds of shell.

Co-precipitated copper zinc oxide catalysts for ambient temperature carbon monoxide oxidation: Effect of precipitate ageing on catalyst activity

A study of the effect of the aging atmosphere on the activity of co-precipitated copper zinc oxide catalysts for the ambient temperature oxidation of carbon monoxide is described and discussed. Four aging atmospheres are reported: air, N2, H2 and CO2, and both the precipitation and the aging of the precipitate were carried out by flowing these gases through the precipitation cell at constant pH and temperature. For all atmospheres, the surface area of the final CuO-ZnO catalyst increases with aging time and, consequently, the specific activity (mol CO converted/g catalyst/h) also increases. However, the intrinsic activity (mol CO converted/m2/h) initially decreases with aging time before attaining a steady level. The highest activity catalysts were obtained using air as the aging atmosphere and TPR studies indicate that this catalyst is less readily reduced. Catalysts prepared using CO2 as the aging atmosphere have lower activity, although the surface areas of these catalysts are not markedly lower. The study demonstrates that selection of the appropriate aging atmosphere, as well as the aging time, is an important parameter for the preparation of co-precipitated catalysts.

A study of the structural and catalytic effects of sulfation on iron oxide catalysts prepared from goethite and ferrihydrite precursors for methane oxidation

A study of the effects of sulfation on the methane oxidation activity of iron oxide catalysts prepared from goethite and 2-line ferrihydrite precursors is presented. Although catalytic performance is found to be dependent upon the precursor, sulfation produces general effects in both systems. Surface area is increased, oxidation activity <400°C is suppressed, and that at 500°C is enhanced leading to the production of selective products. Despite these similarities, sulfation produces different structural effects in the two systems. In the case of iron oxide prepared from goethite, extensive pitting and an increase in disorder in the cationic arrangement are observed. In contrast, a slight increase in crystallinity of the iron oxide prepared from ferrihydrite occurs. The effect of sulfation on catalytic performance is interpreted in terms of a two-site mechanism, complexation poisoning Fe3+ sites active for the lower-temperature oxidation activity with additional sites active at higher temperature being produced.

The relationship between catalyst morphology and performance in the oxidative coupling of methane

A detailed study of the oxidative coupling of methane over magnesium oxide and lithium-doped MgO catalysts is presented. The morphology of a number of different catalysts has been examined by detailed transmission electron microscopy and the results have been correlated with catalyst performance, in particular selectivity to C2 hydrocarbons. Three samples of magnesium oxide have been prepared by different methods. Magnesium oxides prepared from the hydroxide, (ex OH), and from burning magnesium ribbon in air show similar morphology, exposing largely {100} planes; they also show very similar catalytic selectivity and specific activity. The ribbon residue material, however, has a cube length which is greater than that of the ex OH material by a factor of 5–10. Steps and corner sites are therefore present in much greater density on the ex OH sample than on the ribbon residue, and, since catalyst performance is unchanged, it is clear that these sites play no significant part in the catalysis over these materials. The active site is therefore located on the planar {100} surfaces. The most selective magnesium oxide catalyst was prepared by thermal decomposition of magnesium hydroxycarbonate and exposed a greater proportion of higher index mean crystal planes, e.g., {l11}, than the less selective forms of magnesium oxide. It is suggested that an additional selective site is present in this form of magnesium oxide, with density related to morphology but not directly to surface area, perhaps a “bottom step” site. The morphology/performance relationship has also been examined for lithium-doped magnesium oxide catalysts. In agreement with previous studies, addition of lithium causes a loss of surface area and of the morphology characteristic of the precursor magnesium oxide; the grain size also increases, grain boundary dislocations become evident, and dislocations are also observed in the bulk of the grains. These are immobile and of the type 12〉110〈, pinned by the presence of lithium ions. The emergence of a dislocation at the surface of the crystallite provides a locus for [Li+O−] centres, thought to be the active site in methyl radical generation in methane coupling. Similar dislocations are observed in Au/MgO catalysts, which are much less selective to C2 hydrocarbons than is pure MgO.

Methane oxidation using Au/MgO catalysts

A series of Au/MgO(0.04-15 wt%) catalysts have been investigated for the oxidation of methane. Detailed electron microscopy and Mössbauer spectroscopy studies show that two distinct Au morphologies can be observed: (a) two-dimensional Au rafts and (b) discrete three-dimensional Au particles (5-10 nm in diameter). The two-dimensional rafts are observed as the main form of Au at low loadings and, interestingly, these are observed to poison the methane coupling activity of MgO. As the Au loading is increased the proportion of Au present as discrete particles increases and these are considered to be active for methane oxidation to CO and CO2.

On the active site in heterogeneous palladium selox catalysts

The nature of the active site in the Pd-catalysed aerobic selective oxidation of cinnamyl and crotyl alcohols has been directly probed by bulk and surface X-ray techniques. The importance of high metal dispersions and the crucial role of surface palladium oxide have been identified.

Hydrogen production from methane in the presence of red mud –making mud magnetic

Red mud, a waste product of the aluminium industry, has been shown to possess significant activity for the decomposition of methane, a by-product of oil refining and landfill, generating hydrogen and a carbon containing magnetic material. It is envisaged that the latter material could be of interest in terms of downstream purification processes and that its magnetic properties may facilitate separation/handling. In this way, two valuable end products can be generated from two waste products.

Chitosan as a potential amendment to remediate metal contaminated soil — A characterisation study

The potential of chitosan, a fishery waste-based material, as a soil amendment to clean-up metal contaminated soil was investigated. Chitosan was treated using glutaraldehyde (GLA), epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE) as cross-linking reagents to enhance its chemical stability in acidic media and to improve its physical properties. Cross-linking treatment had significant effects on chitosan surface area, pore diameter, surface morphology and crystallinity. Interaction with Ag(I), Pb(II) and Cu(II) decreased the crystallinity of the materials and changed their surface morphology significantly. FTIR analysis confirmed that N and O atoms served as binding sites for the metal ions. Chitosan and treated chitosans were able to bind metal ions, even in the presence of K(+), Cl(-) and NO(3)(-), which are dominant ions in soil. Therefore, remediation of metal contaminated soil using chitosan and cross-linked treated chitosans as soil amendments is feasible.