Open AccessSelective methylation of toluene using CO 2 and H 2 to para -xylene
Author(s) -
Juan Zuo,
Weikun Chen,
Jia Liu,
Xinping Duan,
Linmin Ye,
Youzhu Yuan
Publication year - 2020
Publication title -
science advances
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.928
H-Index - 146
ISSN - 2375-2548
DOI - 10.1126/sciadv.aba5433
Subject(s) - toluene , xylene , p xylene , methylation , chemistry , environmental chemistry , organic chemistry , biochemistry , gene
Toluene methylation with methanol to produce xylene has been widely investigated. A simultaneous side reaction of methanol-to-olefin over zeolites is hard to avoid, resulting in an unsatisfactory methylation efficiency. Here, CO 2 and H 2 replace methanol in toluene methylation over a class of ZnZrO x -ZSM-5 (ZZO-Z5) dual-functional catalysts. Results demonstrate that the reactive methylation species (H 3 CO*; * represents a surface species) are generated more easily by CO 2 hydrogenation than by methanol dehydrogenation. Catalytic performance tests on a fixed-bed reactor show that 92.4% xylene selectivity in CO-free products and 70.8% para -xylene selectivity in xylene are obtained on each optimized catalyst. Isotope effects of H 2 /D 2 and CO 2 / 13 CO 2 indicate that xylene product is substantially generated from toluene methylation rather than disproportionation. A mechanism involving generation of reactive methylation species on ZZO by CO 2 hydrogenation and migration of the methylation species to Z5 pore for the toluene methylation to form xylene is proposed.