Fig. 2 Catalytic performance of toluene methylation using CO2+ H2 or methanol. (A) Influence of the ZZO mass percent in ZZO and 2SZ5 on the product distribution (CO free), toluene conversion, and PX selectivity in xylene. 10%# means that ZZO was directly deposited on Z5 powder. (B) Influence of Z5-modified times by TEOS on the product distribution (CO free), toluene conversion, and PX selectivity in xylene. (C) The comparisons of carbon usage and PX selectivity in xylene via methanol route and CO2 route. (D) Apparent activation energy of toluene by methanol or CO2/H2 route on 4SZ5 or ZZO-4SZ5 catalysts, respectively. Reaction conditions: 360°C; 3.0 MPa; H2/CO2 = 3; gas hourly space velocity (GHSV) of mixture gas (CO2 + H2 + N2) = 12,000 ml g−1 hour−1; toluene vapored at 90°C [weight hourly space velocity (WHSV) of toluene = 1 hour−1]; and time on stream, 15 hours. When using methanol: 3.0 MPa WHSV of toluene = 0.9 hour−1; C7H8/CH3OH = 6, GHSV of mixture gas (H2 + N2) = 12,000 ml g−1 hour−1.
Fig. 3 Structural and acid characterizations of dual-functional catalysts. (A) TEM and (B) SEM images for Z5. (C) TEM, (D) SEM images, and (E) EDS line-scanning profiles for ZZO-4SZ5. a.u., arbitrary units. (F) Pore width distribution of Z5 and ZZO-Z5 series dual-functional catalysts based on the nonlocal density functional theory (NLDFT) method. (G) Ammonia TPD (NH3-TPD) curves of Z5, ZZO, and ZZO-Z5 series dual-functional catalysts according to mass spectrometry signal.
Fig. 4 H2/D2 or CO2/13CO2 isotope effect studies. In situ DRIFTS spectra over the ZZO-4SZ5 catalyst exposed to the stream of (A) C7H8 + CO2 + H2 and subsequently switched to C7H8 + CO2 + D2 and of (B) C7H8 + CO2 + H2 and subsequently switched to C7H8 + 13CO2 + H2. (C) H2/D2 kinetic isotope effect of toluene methylated to xylene using CO2 and H2(D2) over ZZO-4SZ5 catalyst. Reaction conditions are the same as those in Fig. 2.
Fig. 5 The stability test and possible reaction mechanism. (A) Influence of different ZZO and 4SZ5 proximity on Umethy. Reaction conditions are the same as those in Fig. 2. (B) The stability test for ZZO-4SZ5 catalyst. (C) A possible reaction mechanism of toluene methylated with CO2 and H2 over ZZO-Z5 dual-functional catalyst.
Supplementary Materials
Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/34/eaba5433/DC1
Additional Files
Supplementary Materials
Selective methylation of toluene using CO2 and H2 to para-xylene
Jiachang Zuo, Weikun Chen, Jia Liu, Xinping Duan, Linmin Ye, Youzhu Yuan
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