Ammonia formation from nitric oxide over Pd-based catalysts in multicomponent feed gas compositions

Abstract

Using multicomponent gas feeds, the formation of ammonia from nitric oxide over Pd/Al 2 O 3 and Pd/Ce/Al 2 O 3 model catalysts was compared to that of a commercially-available three-way catalyst. Steady-state oxygen-sweep experiments show that the highest activity for ammonia formation is obtained over the Pd/Ce/Al 2 O 3 catalyst whilst the lowest activity is observed for the three-way catalyst. The latter is considered to be linked to the incorporation of rhodium, a component that promotes the NO x reduction selectivity towards N 2. Also, lean/rich cycling experiments were carried out to simulate the cycling conditions that passive-SCR aftertreatment systems depend upon. High activity is again seen over the Pd/Ce/Al 2 O 3 catalyst during short periodic switches. For the three-way catalyst, longer periodic switches are required for the onset of ammonia formation due to the high oxygen storage capacity of this sample as compared to the other two. Hence, a future direction of investigation could be to develop materials with equivalent water-gas shift properties of ceria, but with reduced oxygen storage capacity so as to provide hydrogen for reaction without incurring a significant delay in ammonia formation.

What about the development of catalytic after-treatment processes as part of the transition from vehicles powered by liquid fuels to gaseous fuels

“…In contrast, Pd/Ce/Al 2 O 3 offers the best performances. 129 Useful recommendations for the production and the valorisation of ammonia have been suggested consisting in the installation of a passive ceria-based ammonia-SCR catalyst to promote the water–gas-shift reaction. In parallel, the OSC properties of ceria must be modulated to avoid undesired oxidation reactions.…”

Portable device for generation of ultra-pure water vapor feeds

“…Operational studies require a versatile feed gas delivery system to ensure a gas feed that is well-controlled and variable on demand. In the present case, a laboratory chemical flow reactor, described elsewhere, 29 was used for operational evaluation of the portable water generator device at relatively high flow. Briefly, a total flow of 1000 ml/min, of a desired gas mixture of H 2 and O 2 with argon as balance, was fed through the PWG device by g-MFCs provided by Bronkhorst.…”