David L. Cocke

Planar Models for Alumina-Based Catalysts

Abstract Planar transition aluminas are gaining attention as models for alumina-based catalysts [I] because of their attractiveness for study by modern surface analytical techniques [2], electron optical methods [3], and reflection spectroscopy [4–7]. In this context “planar” means a thin (<10–4 cm) flat oxide layer of uniform thickness. Conventional high surface area aluminas which are used commercially for adsorbents, catalysts, and catalyst supports usually require grinding and /or pressing into disks for characterization by these approaches. This can expose unwanted inner structures or expose the samples to potential contamination by the grinding and pressing tools or uncontrolled atmospheres. In addition, difficulties arise in attempting to study the various stages of alumina development involved with commercial methods since these entail sols, gels, powdered hydroxides, and other inconvenient structures.

Magnesia-supported nickel catalysts. I : Factors affecting the structure and morphological properties

Abstract The effects of calcination and reduction temperature on the metal dispersion of MgO-supported Ni in the ranges 400–800°C and 300–800°C, respectively, have been systematically evaluated by hydrogen chemisorption measurements and comparison has been made with a NiOMgO physical mixture. The role of the bulk Ni x Mg (1 − x ) O solid solution in controlling NiO reducibility and the metal dispersion of Ni/MgO has been ascertained by XPS and ISS investigations. A mechanistic model accounting for the nickel oxide dispersion across the MgO support and the consequent formation of the bulk Ni x Mg (1 − x ) O solid solution has been proposed. A linear relationship between the mean particle size and the reduction temperature, the slope of which increases with Ni loading (2.8–18.0 wt%), has been found. A “multilayer arrangement” of Ni precursor on the support is discussed.

The design and preparation of planar models of oxidation catalysts: I. Hopcalite

At present there exists a need for methods for the preparation of planar models of a variety of heterogeneous catalysts. The preparation of planar models of oxidation catalysts that contain two or more cations represents a considerable challenge. In this paper we report the preparation of a planar model of the very active deep oxidation catalyst, Hopcalite (CuMn2O4), by alloy oxidation. This mixed valent oxide was obtained only after detailed study of the effects of oxidation temperature, oxygen activity, and CuMn alloy composition on the structure and chemistry of the oxide overlayer. In most cases layered structures of Mn oxides and Cu oxides were obtained. Only under a very specific set of conditions could the mixed valent oxide be prepared. The oxidation processes were monitored by X-ray photoelectron spectroscopy (XPS) and from this the structure and chemistry of the overlayers were determined. Hopcalite was identified at the surface by comparison of the XPS spectra with those of a commercial sample and the presence of an unusually low-binding-energy Cu(2p) line in the crystalline CuMn2O4 state. The preliminary catalytic activity of the planar model catalyst is compared with that of the commercial catalyst.

Potential of amorphous materials as catalysts

Abstract Amorphous materials have an important role to play in heterogeneous catalysis. They have several properties which make them of interest both as model catalysts and as real catalysts. A very limited amount of work on their catalytic activities has been done. However, some very interesting results have shown either higher activities or selectivities for amorphous catalysts as compared to their crystalline counterparts. Amorphous metals will be most useful in those reactions having reducing environments such as hydrogenation and isomerization. Amorphous oxides and other nonmetals will be valuable in cracking, oxidation and hydrotreating reactions. Modelling catalysts that are ideal for application of modern surface probes is an exciting development in catalysis research. In amorphous model catalysts, it is extremely important to address the local geometric and electronic structure of active sites on these materials. This research area is ripe for exploitation. The route to the solutions of some long-standing catalytic questions may be through the innovative use of the model amorphous catalysts. This article suggests the potential of the amorphous materials as catalysts, reviews the progress being made and attempts to place amorphous catalysis in perspective with the main stream of catalysis research and development.

An investigation of mercury solidification and stabilization in portland cement using X-ray photoelectron spectroscopy and energy dispersive spectroscopy

Abstract Portland cement doped with 10% by weight aqueous mercuric nitrate was investigated using XPS and EDS. Mercury does not exist as a strong surface specie. The final chemical state of the dopant is believed to be mercuric oxide (HgO). There is no evidence of chemical complexation of Hg in the cement matrix. On the other hand there is evidence of close association of calcium rich deposits with mercury. These calcium deposits show an apparent lack of silicate species when compared to the matrix components. XPS results show that there is marked increase of carbonate content for the doped cement over the undoped cement.

Solidification of hazardous substances‐a TGA and FTIR study of Portland cement containing metal nitrates

Abstract Type I Portland cement samples containing the soluble nitrates of the priority pollutant metals chromium, lead, barium, mercury, cadmium and zinc have been investigated using thermogravimetric and fourier—transform infrared techniques (including diffuse reflectance). The major vibrational bands and thermal stability of the carbonate, sulfate, silicate, water and nitrate species are tabulated and discussed in comparison to uncontaminated Portland cement. The solubility and volatility of mercury in cement and the effect of metal nitrate concentration on the silicate condensation process is discussed. Although results suggest that retardation of cement setting by Zn and Pb salts occurs by limiting hydration, the chemistry of the two processes is distinctly different.

Design of new materials

New Perspectives on Materials Design.- Modifications of Molecular Size and Structure During the Hydrolytic Polycondensation of Metal Alkoxides.- Design of Microstructures in Sol-Gel Processed Silicates.- Inorganic Macromolecules and the Search for New Electroactive and Structural Materials.- The Preceramic Polymer Route to Silicon-Containing Ceramics.- Synthesis of Ceramic Powders and Thin Films from Laser Heated Gases.- New Approaches to the Design of Materials Via Preparative Inorganic Chemistry.- Materials Design by Means of Discharge Plasmas.- Advanced Ceramic Materials and Processes.- Research on Hydrogenated Amorphous Silicon.- Structure and Optical Properties of Amorphous Semiconductors.- Surface Modification by Rapid Solidification Laser and Electron Beam Processing.- Materials-By-Design: Prospects and Promise.- Crystallographic Engineering.- Structure - Property Relationships in Metallic and Oxide Glasses.- Infrared and Raman Studies of Si-Chalcogenide Glasses.- Compound Index.

The surface oxidation and reduction chemistry of zirconium-nickel compounds examined by XPS

Zirconium-nickel intermetallic compounds, Zr2Ni, ZrNi, ZrNi3, Zr2Ni7 and ZrNi5 have been investigated by X-ray photoelectron spectroscopy (XPS) for their response to oxidation and reduction. Chemical and structural changes were found to be composition dependent. Results indicate that preferential reaction, segregation and oxide ordering of one metal component or the other under specific treatment conditions explain the observed catalytic activity of these materials for ethylene hydrogenation.

A model for lead retardation of cement setting

Abstract Lead and chromium doped cement samples have been examined by XPS. Lead has been fiund to be primarily a surface species, unlike chromium. This allows the extension of a model for lead retardation of the setting of Portland cement.

Application of Ion-Scattering Spectroscopy to Catalyst Characterization

Abstract The study of surfaces has evolved in the last decade from a virtually dormant field to one that is vibrant with new ideas and technologies. In the past, the only useful information to be gained from surface techniques was physical in nature, i.e., surface area determination, pore size distributions, film thickness, and surface roughness. No chemical information could be obtained. Today, with the advent of spectroscopic methods, it is possible to gather a variety of information regarding the chemical nature of the surface. Examples of such information include oxidation state determinations, structural effects, and elemental and atomic analysis.