A route to form initial hydrocarbon pool species in methanol conversion to olefins over zeolites

Initial Carbon–Carbon Bond Formation during the Early Stages of the Methanol‐to‐Olefin Process Proven by Zeolite‐Trapped Acetate and Methyl Acetate

“…[14,[38][39][40] In addition to our ssNMR observation (Figure 2a-c), the existence of such neighboring oxygen group-assisted SMS-type species has been characterized by Hunger et al [14,15] and Kondo et al [16,40] Species A' ' eventually led to surface-ethanolic species (B in path a, Scheme 1), which undergoes dehydration (through protonation of alcohol/ether oxygen atoms by Brønsted acid sites of the zeolite) to form ethylene and regenerates ZeOH. [17] In principle,t he presence of two adjacent methoxy groups (Figure 2a-c) could also be consistent with the existence of the oxonium ylide mechanism (Scheme S2). However,c onsidering the reported theoretical calculations based on the oxonium mechanism and the observed carbene/ylide features of SMS in our study,w ef avor the carbene/ylide insertion pathway.…”

“…involves:i )the formation of am ethoxymethyl cation (CH 3 OCH 2 + from SMS and DME) and ii)its subsequent direct CÀCc oupling with another DME or methanol molecule to form CH 3 OCH 2 CH 2 OR (R = H, CH 3 )moiety,which is considered to be ap recursor for olefins. [17] An interesting study was reported by the research groups of CopØret and Sautet, where the formation of the first C À Cbond from DME was proposed to be catalyzed by extra-framework Al atoms in acidic zeolites. [19] Their experimental and theoretically verified proposal involves the CÀCb ond formation over Al 2 O 3 through the CÀHa ctivation of methane in an aluminooxonium (AlO = CH 2 + )/methane adduct, which has conceptual resemblance with the "methane-formaldehyde" mechanism proposed by Hutchings et al, [23] Kubelkova and co-workers [24] and Hirao and co-workers.…”

“…[2,[11][12][13][32][33][34][35] However,t he lack of signals in the 65-90 ppm region signifies the absence of aC H 3 OCH 2 CH 2 OR (R = H, CH 3 )m oiety,a spreviously proposed by Fana nd coworkers. [17] Based on the above-described results,w ep ropose in Scheme 1apathway for the formation of the first CÀCbond during the initial stages of the MTO process.F irst, the CH 3 group of SMS,formed by methylation of aBrønsted acid site (denoted as ZeOH, Scheme 1), interacts initially with another molecule of methanol/DME (Species A in path a, Scheme 1). Them ethyl CÀHo fS MS is then polarized because of its interaction with an eighboring Oa nd the first CÀCb ond formation step is assisted by hydrogen bonding with the CÀH proton (species A in path a, Scheme 1).…”

“…[9] Interestingly,Hunger and co-workers showed already in 2006 that traces of organic impurities neither have any significant influence on product distribution, nor do they govern the formation of HCP species. [10] Since then, the research groups of Hunger, [10][11][12][13][14][15] Kondo, [16] Fan, [17,18] CopØret and Sautet, [19] and Lercher [20] have provided both experimental and theoretical evidences in support of the direct mechanism during the initial stages of the MTO process. Thee arlier proposed direct MTO routes include the a) oxonium ylide,b )carbene,a nd c) methane-formaldehyde mechanisms.…”

Application of Inelastic Neutron Scattering to the Methanol-to-Gasoline Reaction Over a ZSM-5 Catalyst

“…Infrared spectroscopy has been extensively used to investigate species formed when methanol first contacts the zeolite catalyst, and clear evidence obtained for the formation of reactive methoxy groups from reaction of methanol or dimethylether with Brønsted acid sites [8][9][10][11][12]. After longer reaction times at higher temperatures more complex infrared spectra develop which have been assigned variously to adsorbed methylaromatics and olefinic species [12,13].…”