Catalytic Nitrate Removal in a Trickle Bed Reactor: Direct Drinking Water Treatment

Palladium (Pd)-based catalysts hold promise as an alternative water treatment technology for nitrate (NO3-), but practical application requires a flow-through reactor that efficiently delivers hydrogen (H-2) from gas to water. A trickle bed reactor (TBR) packed with a 0.1 percent by weight (wt%) Pd-0.01 wt% In/gamma-Al2O3 (indium and porous aluminum oxide) catalyst was evaluated to address this challenge. Catalytic activity generally increased with H-2 superficial velocity (0.65-29.6 m/h) and liquid (deionized water) superficial velocities from 14.8 to 26.6 m/h before decreasing at 38.5 m/h. This decrease corresponded to a change in flow regime and suggests that optimal TBR performance occurs at the transition from pulse to bubble flow. An optimal TBR activity of 19.5 +/- 1.3 mg NO3-/min-g Pd was obtained; this is only similar to 18% of the batch reactor activity as a result of H-2 mass transfer limitations, but three to 15 times greater than activities obtained with previous flow-through reactors. Catalyst deactivation occurred in the TBR after 41 days of operation, motivating the need for improved fouling mitigation strategies.