Coking and regeneration of palladium-doped H3PW12O40/SiO2 catalysts

The coking during propene oligomerisation and subsequent regeneration of bo th silica-supported heteropoly acid H3PW12O40 (PW) and its palladium-modifi ed form (1.6-2.5 wt% Pd) have been studied. P-31 MAS NMR studies have revea led that the Keggin structure of the catalyst was unaffected by coke deposi tion in both unmodified PW/SiO2 and Pd-modified form. As shown by C-13 MAS NMR and TGA/TPO, the Pd modification affects the nature of the coke formed: for the standard catalyst (PW/SiO2) both soft coke, comprising mainly high molecular weight aliphatic oligomers, and hard coke, comprising polynuclea r aromatics, are formed whilst on the Pd-modified catalyst only the soft co ke is observed. Coke formation causes strong deactivation of the catalyst i n the oligomerisation of propene. The aerobic burning of coke on the unmodi fied PW/SiO2 occurs in the temperature range of 470-520 degrees C. Doping t he catalyst with Pd significantly decreases this temperature to allow catal yst regeneration at temperatures as low as 350 degrees C without loss of ca talytic activity.