SULFUR DEACTIVATION IN NO REDUCTION BY NH3 .1. RATES OF REDUCTION BY NH3 AND H-2

The effect of So2 and H2S on steady-state reaction rates for the catalytic reduction of NO by NH3 and by H2 over precious metal catalysts supported on Al2o3 was determined in a differential, plug-flow microreactor, between 473 and 685 K at 1 atm total pressure with a feed of 1.0% NO, and 1.0% NH3 or H2, in He. The order of NO reduction activity by NH3 for the catalysts with sulfur-free feed at 473 K was: Pt ~ Pd » Ru > Pt-Ni ~ Ni. Fifty ppm of So2 in the feed gas so severely deactivated supported Pt, Pd, and Ni that a temperature increase of more than 200 K was required to achieve a measurable rate of reaction. Moreover, the activity sequence was completely re-ordered to: Ru >>> Pt-Ni » Pt, Pd, Ni. The activity of Pt-Ni was several orders of magnitude greater than that observed for either of the metals independently. Ruthenium was 106 times more active than Pt or Pd, although it was about two orders of magnitude less active than Pt at 473 K without So2 in the feed gas. Hydrogen sulfide at 50 ppm was only 1/5 as effective as the same level of So2 in deactivating Pt but was 400 times more effective than So2 or in deactivating Ru/Al2o3. With hydrogen as a reductant the activity sequence in the presence of 50 ppm of So2 was Ru » Pt-Ni > Pt. © 1979, American Chemical Society. All rights reserved.