Chemisorption-titration, as a surface sensitive analysis method, is widely applied for direct measurement of specific surface area of metallic clusters on heterogeneous catalysts. However, on active oxide supports, the products yield of this method is strongly affected by the exchanging of oxygen between the support and the titration gases. In this study, Pt and Cu based catalysts are used as the source for metallic sites characterizations through isothermal titration experiments within a wide temperature range. Pt/Fe2O3 catalysts were characterized using CO oxidation and Cu/CeO2 catalysts were characterized using N2O decomposition. The titration products are CO2 and N2 respectively. Detailed measurements requires instant online mass spectroscopy characterization and temperature control from subzero to room temperatures, for this purpose an online micro reactor is developed and applied for quantitative products calibration. For both series of catalysts, MS signal are also measured on pure metallic powder and calibrated with commercial chemisorption measurement system. The temperature dependence of both total titration products from the supported samples reveals that for each catalyst, there are narrow subzero temperature windows that the titration products are only related with metallic sites. The results provides an approach towards an one-step chemisorption-titration procedure for measurement of dispersion on active oxide supported catalysts, which is a possible benchmark that bridges fundamental model catalysts and industrial applied catalysts in performance evaluation.

Applying low temperature titration for determination of metallic sites on active oxide supported catalysts

2019 Fall National Meeting

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