(113c) Catalytic Reforming On Hexaaluminate Based Catalyst Supports

This work reports the synthesis, characterization and performance of reforming catalysts based upon dispersed Rh clusters on hexaaluminate supports. Two different hexaaluminates were prepared, one with a Ca substitution and one with a strontium substitution. The hexaaluminates are synthesized with a co-precipitation process and the Rh was added via incipient wetness technique. As controls, 3 other common supports are examined in this work, Yttria-stabilized zirconia (YSZ), gadolinium doped ceria (GDC), and gamma Al2O3. The resulting structures of all supports are characterized using X-Ray diffraction (XRD) and scanning electron microscopy (SEM). Support surface area is measured by BET and metal dispersion is measured using pulsed CO chemisorption.

A stagnation-flow reactor is used to measure catalytic activity. In these experiments, the catalyst is applied to a flat surface that is held at a fixed temperature. Reactive gases (methane, steam or CO2, and diluent) impinge on the catalytic stagnation surface. Microprobe mass spectrometry is used to measure gas-phase species profiles in the boundary layer normal to the catalyst surface. These experiments are interpreted with chemically reacting flow models that incorporate elementary heterogeneous mechanisms.

BET results indicate that the Sr and Ca-substituted hexaaluminates provide a stable support structure for Rh that resists surface area loss under accelerated aging conditions. Rhodium supported on Sr-substituted hexaaluminates is also found to perform well for the steam and dry reforming of methane. This paper reports comparisons between predicted and measured gas-phase boundary-layer profiles. A previously developed detailed reaction mechanism is used. Despite the fact that the mechanism was developed for Rh-Al2O3 catalyst-support system, it performs remarkably well for the current hexaaluminate-supported system