Syngas to light olefins over ZnAlOx and high-silica CHA prepared by boron-assisted hydrothermal synthesis

摘要

Transformation of syngas into light olefins (STO) over bifunctional oxide and zeolite (OX-ZEO) composite catalysts requires rational design of zeolites with moderate to low acid density and strength. As a promising zeolite component in OX-ZEO towards olefins production, the synthesis of CHA with desirable acidity remains to be a challenging task. Herein, high-silica CHA zeolite with Si/Al ranges from to 20 to infinity were prepared via a boronassisted hydrothermal synthesis method. The influence of Si/Al ratio on the acidity and textural properties of boron-containing CHA (BAl-CHA) was systematically studied. The syngas to olefin performance over ZnAlOx/ BAl-CHA was explored. The roles of acidity, framework boron and reaction parameters in determining the olefin selectivity as well as catalyst stability were revealed. The 85.1% selectivity of light olefins was achieved over the BAl-CHA catalyst with Si/Al ratio over 300. The boron played a vital role in directing the formation of CHA structure (Si/Al > 100) and reduced the strong acid sites. The H2/CO ratio, reaction temperature, total pressure and proximity of the two components also played crucial role in determining the light olefins selectivity. A DME/ methanol involved aromatic-cycle is proposed to play a predominant role in the olefin production. The residual CO and H2 are likely involved in the aromatic-cycle, and then affect the product distribution, with CO promoting the ethene selectivity while H2 enhancing the alkane selectivity.

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