Philip A. Barnes

A new approach to the statistical optimisation of catalyst preparation

Abstract The statistical design of experiments is not widely used due to the apparent complexity of the procedures involved. A simplified approach, based on the methods of Taguchi, is described and is illustrated by applying it to the optimisation of the preparation of a metal-carbon catalyst. The surface area was increased from 8 to 250 m 2 g −1 . It is shown that the method gives five significant advantages. It enables the amount of experimentation to be significantly reduced; it provides a means for assessing the significance of synergistic effects (interactions) between variables (factors) and it can yield evidence for the existence of previously unsuspected interactions. The method has the advantage of being applicable to existing production processes by assessing the consequences of variations in operating parameters found within normal run conditions. Finally, the experimental design process is simplified and the analysis of results is facilitated by the ready availability of the required statistical techniques in commercial software for microcomputers.

An investigation of the porosity of carbons prepared by constant rate activation in air

Nutshell carbon was activated in air/N2 mixtures using controlled rate (CR) methods and the porosity characteristics compared with carbons activated conventionally in CO2 at 800 °C to the same degree of burn off. The advantages of CR activation in air include the use of lower temperatures and the avoidance of thermal runaway. It was also possible to prepare activated carbons with significant microporosity, showing that excessive external burn off was prevented. In the CR experiments, the rate of evolution of CO2 was controlled and constrained at a set level, either by altering the furnace temperature or the concentration of air in the activating gas. Although the highest micropore volumes (0.4 cm3 g−1) were obtained at 40% burn off with the conventional method, at 20% burn off, the CR method using air concentration to control CO2 evolution yielded carbons with similar micropore volumes (0.2 cm3 g−1) to those activated conventionally.

High temperature ceramics for use in membrane reactors: the development of microporosity during the pyrolysis of polycarbosilanes

The pyrolysis of polycarbosilane (PCS), a ceramic precursor polymer, at temperatures up to 700 °C under an inert atmosphere results in the development of amorphous microporous materials which have a number of potential applications, such as gas separation membranes. This paper investigates the development of microporosity during pyrolysis under nitrogen, at temperatures ranging from 300 to 700 °C, of both the cross-linked and non-cross-linked starting materials. The products are characterised by nitrogen adsorption, to determine surface areas and pore volumes, solid-state NMR, electron microscopy and FTIR, and their formation is studied using thermal analysis and evolved gas analysis with on-line mass spectrometry. The cross-linked and non-cross-linked PCSs have a maximum micropore volume of 0.2 cm3 g−1 at pyrolysis temperatures of between 550 and 600 °C. The microporosity is stable in air at room temperature, but is lost in oxidising atmospheres at elevated temperatures.

The application of CRTA and linear heating thermoanalytical techniques to the study of supported cobalt oxide methane combustion catalysts

Two combined thermal analysis-mass spectrometry techniques have been used to ascertain the effects of various support materials on the preparation and subsequent combustion activity of supported cobalt oxide catalysts. Both techniques used small sample masses in order to minimise temperature and pressure gradients throughout the sample during reaction as the sample temperature was increased at a linear heating rate. Temperature-programmed reduction (TPR) techniques employed not only reveal reduction, but also distinguish it from the adsorption (or evolution) of the H2 and the loss of absorbed water. The thermally induced decomposition of supported and unsupported cobalt nitrate hexahydrate was studied using a solid insertion probe mass spectrometer (SIP-MS) system operating under high vacuum. The support material was found to affect the decomposition process significantly. In particular, the decomposition of cobalt nitrate dispersed on γ-Al2O3 occurred via a markedly altered process in comparison with the unsupported nitrate. The ZrO2 and CeO2 supports both exhibited less pronounced effects on the decomposition process. After calcination of dispersed cobalt nitrate species, methane combustion activity was found to be much lower for alumina-supported samples relative to the other supports used. A combined temperature-programmed reduction–mass spectrometry (TPR–MS) technique was used to elucidate a correlation between catalyst activity and reducibility. The reduction of a Co3O4/CeO2 catalyst was also studied under constant rate thermal analysis (CRTA) conditions.

Development of a new instrument for performing microwave thermal analysis

This article describes the design and operation of a new thermal analysis instrument which uses microwaves to simultaneously heat and detect thermally induced transformations in samples with masses in the range of 50 mg to 0.5 g. The data acquisition and control software developed for the instrument support a range of experimental techniques including constant power, linearly ramped power, linearly ramped temperature, and various modulated methods. Microwave thermal analysis utilizes the fact that physical or chemical alterations in a material, caused by processes such as melting, decomposition, or solid-solid phase changes, cause variations in its dielectric properties. These can be revealed by a variety of means including changes in the sample temperature, the differential temperature, or the shape of the power profile during linear heating experiments. The scope of the instrument is demonstrated with the decomposition of basic copper carbonate. The large temperature increase (∼100 °C) observed on the f...

Qualitative and quantitative aspects of microwave thermal analysis

Thermally induced transformations in materials (e.g. melting, decomposition or solid‐solid phase changes) alter their dielectric properties and hence their ability to interact with a microwave field. This paper describes a new technique, microwave thermal analysis, where microwaves are used both to heat a material and as a means of detecting thermal transitions. Two approaches are described. The first is based on the changes in the temperature of a material when subjected to a constant microwave power and the second on the microwave power profile obtained when a material is heated in a controlled (linear) manner. Both approaches can provide qualitative and quantitative information on solid state processes. A classification is proposed for the different types of results found for various materials and transitions. The advantages and limitations of studying transitions and reactions using microwave energy are discussed. # 2000 Elsevier Science B.V. All rights reserved.

Preparation, Characterisation and Application of Metal-doped Carbons for Hydrogen Cyanide Removal

A novel method for the production of metal-doped activated carbons was developed. Evaluation of the materials produced showed that the metals were well dispersed throughout the carbon pore structure and had a high degree of accessibility. The filtration performance of these materials was assessed against HCN using inverse gas chromatography. The performance was affected both by the selection of metals and the conditions used in the production of the carbon. In-depth studies varying the synthesis parameters were performed with the aim of optimising the manufacturing process. Significant HCN adsorption capacity was developed which exceeded that of the current best available ASC-type carbons.

Microwave Thermal Analysis - A New Approach to the Study of the Thermal and Dielectric Properties of Materials

This paper describes a new instrument for performing thermal analysis using microwaves both as a form of heating and as a novel means of detecting thermally induced transformations in materials. Results are presented for a selection of processes including decompositions, dehydrations and phase changes. The capability of the instrument to be coupled with ancillary techniques such as EGA is also demonstrated.

A Study of the Activation of Carbon Using Sample Controlled Thermal Analysis

A constant rate method involving the control of the concentration of evolved CO2 at a constant level was used to study the air activation of pure and copper-doped carbon prepared from sodium carboxymethylcellulose. Whereas under a linear heating regime, both types of carbon reacted suddenly and quickly with O2, under constant rate conditions this violent reaction was avoided and oxidation proceeded steadily at a lower temperature until complete burn off of the carbon was achieved. The catalytic effect of the copper on carbon gasification was noted with lower reaction temperatures for both linear heating (380°C compared to 500°C) and for the constant rate experiments (320°C compared to 400°C).

Real-time analysis of peak shape : a theoretical approach to sample controlled thermal analysis

Abstract This paper describes a theoretical framework, based on real-time analysis of the shape of thermoanalytical peaks, for two new approaches to sample controlled thermal analysis (SCTA). These new methods have the common aim of effecting changes in the heating rate at a given point in a process (i.e. at a set value of α) irrespective of the absolute magnitude of the peaks produced by that process. This permits the automatic on-line optimisation of the resolution/experiment time ratio without the need for preliminary experiments.