Portal de Periódicos da CAPES

Evolution of C–C Bond Formation in the Methanol-to-Olefins Process: From Direct Coupling to Autocatalysis

2018; American Chemical Society; Volume: 8; Issue: 8 Linguagem: Inglês

10.1021/acscatal.8b02385

2155-5435

Xinqiang Wu, Shutao Xu, Yingxu Wei, Wenna Zhang, Jindou Huang, Shuliang Xu, Yanli He, Shanfan Lin, Tantan Sun, Zhongmin Liu,

Advanced NMR Techniques and Applications

Methanol conversion during the induction period of methanol-to-olefin (MTO) process has been investigated by solid-state nuclear magnetic resonance (ssNMR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), gas chromatography–mass spectroscopy (GC-MS), and time-of-flight mass spectroscopy (TOF-MS), over HSAPO-34 molecular sieve. The two-dimensional (2D) 13C–13C MAS NMR spectra revealed the correlation of surface methoxy species (SMS) and dimethyl ether (DME)/methanol was enhanced with the temperature increase, supporting that the carbon–carbon (C–C) bond can be possibly formed through the direct coupling of SMS and the surface-adsorbed C1 reactant. The evolution of surface species was monitored continuously by the aid of in situ ssNMR and in situ DRIFTS. With the consumption of SMS, alkenyl or/and phenyl carbocations were formed and accumulated as the successive intermediates for methanol conversion. Based on these direct observations, we propose that the first C–C bond is derived from SMS-mediated DME/methanol activation while alkenyl/phenyl carbocations can take over SMS and convert methanol efficiently in the autocatalysis stage of the MTO process.