In situ infrared spectroscopy under hydrothermal conditions : application for aqueous phase reforming

Abstract

Development of an efficient catalyst in heterogeneous catalysis includes understanding the relationship between catalyst structure and its activity. In situ spectroscopy methods can be used to study structure of the catalytic active site and reaction sequences under reaction conditions. Information obtained from such analyses, e.g. the structure of the surface species responsible for catalyst deactivation or the changes in catalyst structure under the reaction conditions, can suggest routes for catalyst improvement. However, the limited applicability of the techniques in real reaction conditions and especially in the presence of a solvent can be a challenge for in situ investigations. Attenuated Total Reflection Infrared (ATR-IR) spectroscopy, discussed in detail in this thesis, is a technique used for studies at solid/water interface. The main target of the work is applicability of the ATR-IR spectroscopy for in situ studies of the water/catalyst interface in Aqueous Phase Reforming (APR). APR reaction requires high temperatures and pressures (150 - 350 °C and 10 - 50 bar), therefore a suitable ATR-IR cell had to be designed and tested for these conditions. Results describe the design of an in situ ATR-IR Tunnel cell with a cylindrical Element coated with a catalyst layer. Hydrodynamic flow simulations showed non-plug flow behavior in the cell. Applicability of ATR-IR spectroscopy under APR conditions was demonstrated by studying the conversion of -Al2O3 to boehmite in real-time under hydrothermal conditions of APR, showing that this transformation leads to catalyst deactivation together with Pt sintering and blockage of the Pt surface with boehmite. The formation of boehmite was established by Raman spectroscopy and 27Al MAS NMR analysis of samples before and after exposure to APR conditions. The adsorption of hydroxyacetone on Pt/AlO(OH) and Pt/ZrO2 catalysts at 230 °C/ 30 bar was also studied by in situ ATR IR spectroscopy. Formation of aldol condensation products of hydroxyacetone strongly adsorbed on the surface was observed on Pt/ZrO2 and ZrO2 in contrast to Pt/AlO(OH) and AlO(OH). The amount and type of coke deposits determined by elemental analysis and TPO showed that coke with low oxidation temperatures was deposited mostly on the surface of the ZrO2 support.