Wall-loaded Pt/TiO2/Ti catalyst and its application in ammonia oxidation reaction in microchannel reactor

Abstract

A microchannel reactor is a promising reactor type for industrial applications. However, loading heterogeneous catalysts in the microchannels is troublesome because of the high pressure drop and serious fluid flow abrasion. In this research, a home-made microchannel reactor was designed by using a wall-loaded Pt/TiO₂/Ti catalyst as the microchannel wall. This wall-loaded Pt/TiO₂/Ti catalyst was prepared by anodizing a Ti foil and photodepositing Pt on the anodic surface layer. The foil was then assembled as a side wall of the microchannel. Ammonia oxidation was used as the probe reaction for evaluating the performance of this microchannel reactor by using the wall-loaded catalyst. Simulation and experimental results show that 100% ammonia conversion can be obtained under the following conditions: temperature, 300 °C; gaseous hourly space velocity, 35 000 h⁻¹; catalyst loading percentage, 85% of the total channel area; and ammonia to oxygen volume ratio, 1 : 13, in the absence of nitrogen, with a microchannel of length 80 mm, width 1.0 mm, and height 0.3 mm. Pressure drop in the microchannel is as small as 1.18 kPa, and temperature distribution is relatively uniform. Notably, NO_x selectivity is significantly improved to become 88.32% at 300 °C. Simulations confirm that the selectivity showed such a high improvement owing to the short residence time of NO_x because of the unique blind-hole structure of TiO₂ nanotubes and the resulting large mass transfer resistance. The operation of this reactor with the wall-loaded Pt/TiO₂/Ti catalyst is stable without any remarkable performance decay even after 360 h of operation. Hence, the microchannel reactor with a wall-loaded catalyst on the anodic metal is an attractive prospect for large-scale applications of rapid gas-to-solid exothermic reactions.