The guiding role of pre-coking on the coke deposition over ZSM-5 in methanol to propylene

Abstract

Deposition of carbonaceous compounds was used to improve the propylene selectivity of ZSM-5 by deactivating some acid sites meanwhile maintaining the high activity for methanol conversion. The carbonaceous species of pre-coked samples before and after MTP reactions were investigated by elementary analysis and thermogravimetric analysis (TGA). The results showed that pre-coke formed at low temperature (250°C) was unstable and easy to transform into polyaromatics species at the high reacting temperature, while combining 5% pre-coking process with 95% steam treatment at high temperature (480°C) was effective in inhibiting the formation of coke deposits and presented a significant improvement in the propylene selectivity.

Carbonaceous deposits on cobalt particles reverse the catalytic patterns in butadiene hydrogenation

“…In other cases, the beneficial roles of carbonaceous deposits in heterogeneous catalysis have also been documented in several transformations, including alkane dehydrogenation, 32 methanol-to-hydrocarbon conversion, 33,34 selective hydrogenation, 35 etc., which have been discussed in an excellent review by Collett and McGregor. 36 In this context, coke deposits can act as new catalytic centers in dehydrogenation or participate in catalytic cycles (H transfer in zeolite-catalyzed methanol conversion).…”

“…36 In this context, coke deposits can act as new catalytic centers in dehydrogenation or participate in catalytic cycles (H transfer in zeolite-catalyzed methanol conversion). [32][33][34] The selective deactivation of non-selective surface sites in hydrogenation has been proposed as the main cause for the improved selectivity. A noteworthy example is the formation of PdC x during alkyne hydrogenation to alkenes.…”

“…In other cases, the beneficial roles of carbonaceous deposits in heterogeneous catalysis have also been documented in several transformations, including alkane dehydrogenation, 32 methanol-to-hydrocarbon conversion, 33,34 selective hydrogenation, 35 etc. , which have been discussed in an excellent review by Collett and McGregor.…”