Oxidative dehydrogenation monolithic catalysts

Combinatorial chemistry can perhaps help discover new catalyst formulations for reactions presently of particular interest, such as oxidations or ammoxidation, and generally all reactions of alkanes. Reactions traditionally made in different kinds of processes are frequently shown to be also activated by heterogeneous catalysts (e.g., epoxidations). Reactors of unexpected design allow surprisingly selective reactions (e.g., monoliths for the oxidative dehydrogenation of light alkanes). However, the distance often remains long between these discoveries and the manufacture of active and selective catalysts adequately structured for particular use in an industrial reactor inserted in an industrial plant. 

Schmidt s group discovered another important class of very fast reactions — the oxidative dehydrogenation of olefins over monolith catalysts. For ethane, the reaction is... 

Very high olefin yields were reported by Schmidt and co-workers,who first proposed the oxidative dehydrogenation of hght alkanes over insulated noble metal coated monoliths at contact times of a few milhseconds. This new concept of catalytic reactor had been previously applied by the same group to methane partial oxidation and was extended to test the reactivity of C2-C6 alkane/air fuel-rich feeds. Ceramic foam monoliths (with 45 and 80 ppi) were mostly studied as supports of noble metals and bimetallic catalysts. 

Table 28.3. Oxidative dehydrogenation of propane over different catalysts (Pt/10%Rh gauze, VMgO and Pt/monolith catalysts) at few milliseconds contact time. Adapted from Ref. 56.

Shi X, Ji S, Wang K, Li C (2008) Oxidative dehydrogenation of ethane with CO2 over novel Cr/SBA-15/Al203/FeCrAl monolithic catalysts. Energy Fuel 22 3631-3638... 

The authors proposed that the role of the catalyst was that of providing thermal ignition (through non-selective oxidations to COx) to the gas-phase process responsible for the formation of olefins. TAP (temporal analysis of products) studies at low temperatures supported this picture and confirmed that carbon oxides, hydrogen and methane were the main products of the surface reaction mechaiusm over a Pt/Al203 catalyst. Ethane ODH experiments with a co-feed over H2 were perfomed over Pt-Sn coated monoliths and confirmed the very high selectivity of this process concept toward olefins, due to the combination of the selective combustion of H2 (the co-fuel) and the dehydrogenation of ethane. ... 

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