Analysis of Ru/La-Al2O3 catalyst loading on alumina monoliths and controlling regimes in methane steam reforming

In this work Ru (1.5 wt%)/La (3 wt%)-modified-Al2O3 coated α-alumina monoliths of different geometries (100 cpsi square channel, 170 cpsi hexagonal channel, diameter 9 mm, length 30 mm) were prepared by in-situ catalyst washcoating technique with catalyst loadings in the range 100 – 250 mg. The powder and structured catalysts were characterized by various physio-chemical characterization techniques: particle size distribution, zeta potential, slurry viscosity, N2 physisorption, H2 chemisorption, X-ray diffraction, washcoat adherence, optic and scanning electron microscopy. The influence of catalyst loading was investigated on geometric, hydraulic and catalytic performance towards methane steam reforming (SMR) reaction by varying temperature (600 – 900°C), weight hourly space velocity (WHSV = 27 – 368 NL h-1 gcat-1) at fixed molar steam to carbon ratio (S/C = 3.0). Well adhered and uniform catalyst layers were achieved with stable catalytic performance towards methane steam reforming. Characteristic time analysis and dimensionless numbers were utilized to identify the controlling regime in catalytic monoliths. The values of optimum washcoat thickness for 100 cpsi and 170 cpsi monoliths are found to be 58.5 μm and 78.9 μm respectively. SMR is reaction controlled for 100 -150 mg catalyst loaded monoliths. No external diffusion control regime is observed. At higher catalyst loadings (> 200 mg) SMR is influenced by washcoat diffusion limitation and availability of less contact time for the reaction, suggesting the use of higher cell density monoliths with smaller hydraulic diameter, and higher geometric surface area.