Henrik Kusar

Catalytic combustion of methane over bimetallic catalysts a comparison between a novel annular reactor and a high-pressure reactor

Abstract The effects of adding a co-metal, Pt or Rh, to Pd/γ-Al2O3 catalysts were studied with respect to the catalytic activity for methane combustion and compared to a Pd/γ-Al2O3 catalyst, using both a pressurized pilot-scale and a lab-scale annular reactor. Temperature programmed oxidation (TPO) experiments were also carried out to investigate the oxygen release/uptake of the catalyst materials. Palladium showed an unstable behavior both in the pilot and lab-scale experiments at temperatures well below the PdO to Pd transformation. An addition of Pt to Pd stabilized, and in some cases increased, the catalytic activity for methane combustion. The TPO experiments showed that the oxygen release peak was shifted to lower temperatures even for low additions of Pt, i.e. Pd:Pt=2:1. For additions of rhodium only small beneficial effects were seen. The steady-state behavior of the lab-scale annular reactor correspond well to the pressurized pilot-scale tests.

Deactivation of high temperature combustion catalysts

The main objective of catalytic combustion is to attain a flame temperature 300–400 K lower than in thermal or non-catalyzed combustion; this substantially reduces the direct combination of nitrogen and oxygen in air to form the so-called thermal NOx. In this way, catalytic combustion is a preventive solution to the problem of nitrogen oxides emissions. The focus of attention here is its application in gas turbines, both for power production and for transportation by road, sea and air. Any catalyst for catalytic combustion, however, has to face extreme demands: continuous operation above 1000 ◦ C in the presence of oxygen and steam for preferably 30,000 h, resistance to poisons in the fuel and/or process air, and ability to withstand large thermal and mechanical shocks. While material/catalyst advances are still inadequate, systems engineering is coming to the rescue by developing multiple-monolith catalyst systems and the so-called hybrid reactors. The deactivation of catalyst supports, washcoats, and active materials is briefly reviewed here: sintering, vaporization, phase transformation, thermal shock and poisoning.