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The carbonylation reaction of ethane with CO to produce carboxylic acid was studied over zinc-modified ZSM-5 zeolite (denoted as Zn/ZSM-5) using in situ solid-state NMR spectroscopy. 13 C-isotope-labeled reactants were alternatively used to monitor the co-reaction at temperatures of 298–623 K. The NMR experimental results demonstrated that surface zinc-ethyl and methoxy species were formed and identified as key intermediates in the reaction. The reactivity of these intermediates was further explored under both oxidizing and reducing conditions by adding O 2 and H 2 into the reaction system. It was found that ethane was initially activated into zinc–ethyl species that show reactivity similar to that of organometallic compounds such as diethyl zinc. The interaction of zinc–ethyl species with CO 2 resulting from the oxidation of CO produces propanoic acid. Side products such as aromatics were formed by dehydrogenation of zinc–ethyl species via the formed ethene intermediates. We also found that hydrogenolysis of ethane occurred and gave rise to byproduct methane, which led to the formation of acetic acid by carboxylation with CO 2 . Additionally, CO was converted into surface methoxy species, which could react with CO to produce acetic acid via a Koch-type carbonylation reaction. [ABSTRACT FROM AUTHOR]

The formation and reactivity of a methylbenzenes (MBs) hydrocarbon pool in the induction period of the methanol-to-olefins (MTO) reaction over zeolite H-ZSM-5 was investigated and the mechanistic link of MBs to ethene and propene was revealed. Time evolution analysis of the formed MBs and 12 C/ 13 C methanol-switching experiments indicate that in the induction period bulkier compounds such as tetraMB and pentaMB have higher reactivity than their lighter counterparts such as p/m-diMB and triMB. By correlating the distribution of MBs trapped on H-ZSM-5 with ethene and propene, we found that tetraMB and pentaMB favor the formation of propene, while p/m-diMB and triMB mainly contribute to the formation of ethene. On the basis of this relationship, the olefin (ethene and propene) selectivity can be controlled by regulating the distribution of trapped MBs by varying the silicon-to-aluminum ratio of ZSM-5, reaction temperature, and space velocity. The reactivity of MBs and the correlation of MBs with olefins were also verified under steady-state conditions. By observation of key cyclopentenyl and pentamethylbenzenium cation intermediates using in situ solid-state NMR spectroscopy, a paring mechanism was proposed to link MBs with ethene and propene. P/M-diMB and triMB produce ethylcyclopentenyl cations followed by splitting off of ethene, while tetraMB and pentaMB generate propyl-attached intermediates, which eventually produce propene. This work provides new insight into the MBs hydrocarbon pool in MTO chemistry. [ABSTRACT FROM AUTHOR]