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Surface characterization of some selected zinc oxide samples IV: Zinc oxide prepared by the thermal decomposition of zinc basic carbonate

1983; Elsevier BV; Volume: 18; Issue: 3 Linguagem: Inglês

10.1016/0376-4583(83)90055-9

1878-1063

A.M. Khalil, Stein Kolboe,

Carbon Dioxide Capture Technologies

Zinc oxide samples were prepared by the thermal decomposition of zinc basic carbonate at different temperatures in the range 135 – 500 °C. The arbitrary temperatures were selected using thermogravimetric analysis. The weight lost at these temperatures (i.e. the isothermal weight loss) was also determined. Nitrogen adsorption measurements were carried out on the different samples; specific surface areas, total pore volumes, average pore radii and other surface parameters were estimated and interrelated. From the thermogravimetric analyses the thermogravimetric losses appeared to be larger than the isothermal weight losses for all the selected temperatures. Contrary to the behaviour expected, this has been interpreted using detailed pore structure studies, an analysis for surface areas located in wide pores and pore volume distribution curves. It is reported that some of the decomposition products (water plus carbon dioxide) are strongly held in micropores (or narrow pores) and this directly influences the estimated surface areas as well as the heat of adsorption (as indicated by the magnitude of the Brunauer-Emmett-Teller (BET) C constant). The fractional volume of micropores and the reciprocal of the average pore radius vary similarly when they are graphically presented as functions of the decomposition temperature; this might be considered indicative of the extent of physisorption of adsorbate molecules. Correspondingly, the similarity between changes in core volume and the slope of the nS-nR plot (if they are graphically presented as functions of the decomposition temperature) is a tentative measure of the availability of physisorbed molecules to be chemisorbed. The sequence of these two processes is related to the decomposition mechanism of zinc basic carbonate. It was found from this investigation that the zinc oxide samples possess high surface areas accompanied by low BET C constants. The chemisorption process of different alcohols is primarily controlled by the volume of cores. The catalytic dehydrogenation reactions of alcohols is controlled by the extent of the surface, as well as the capability for chemisorption; all these variables are controlled by the thermal treatment conditions.