A Stable Zinc Zeolite Catalyst for Dehydrogenation of Ethane to Aromatics and Ethylene

Discrimination of the Synergistic Effect of Different Zinc Active Sites with a Brønsted Acid in Zeolite for Dehydrogenation Cracking of n-Octane and Ethane Dehydroaromatization

The synergetic effect of different zinc active sites with a Brønsted acid site (BAS) in Zn-MCM-22 for n-octane dehydrogenation cracking and ethane dehydroaromatization was investigated. Zn-MCM-22 catalysts containing ZnO were prepared via incipient wetness impregnation (IM) using liquid ion grafting, whereas those containing [ZnOx]2+ were prepared via atom-planting (AP) using the gas dechlorination reaction. The synergetic effects of BAS with micropore incorporated [ZnOx]2+ and external surface ZnO species on the dehydrogenation of different molecule size reactants n-octane and ethane were compared. The synergistic effect of ZnO and BAS can improve ethane dehydrogenation through aromatization, whereas [ZnOx]2+ as the introduced Lewis acid site (LAS) can override the bridge Si-OH-Al hydroxyl group BAS to inhibit the generation of benzene-toluene-xylene (BTX) and is more favorable for ethane dehydrogenation. The AP method can effectively regulate the n-octane dehydrogenation cracking product distribution by adjusting the volatilization time of ZnCl2 vapors to regulate the ratio of LAS/BAS in zeolites. The kinetic analysis was used to correlate the roles of the [ZnOx]2+ site and BAS in the dehydrogenation, hydrogen transfer, and cyclization reactions of n-octane and ethane, respectively. Moreover, the hydroxyl group grafted [ZnOx]2+ sites have better activity and stability for higher temperature dehydrogenation.

Biodiesel-Derived Waste Glycerol as a Green Template for Creating Mesopores in the ZSM-5 Catalyst for Aromatics Production Applications

The present study provides a novel sustainable approach for the synthesis of the ZSM-5 catalyst using biodiesel-derived waste glycerol as a green template as well as a mesopore creator, which is here reported for the first time, to the best of our knowledge. The use of bioglycerol in the preparation of ZSM-5 (Zn-Z-G and Zn-Z-T) materials exhibited a typical MFI zeolite structure, indicating glycerol played a similar role to that of a typical (TPA+) template in the formation of the ZSM-5 zeolite structure. The Zn-Z-G material also exhibited a large mesopore in the ZSM-5 pore structure, suggesting that glycerol played both template and mesopore creator roles. Interestingly, Zn-Z-GT prepared by the dual-template route using bioglycerol along with typical TPA+ showed a MFI zeolite structure with special catalytic features such as hierarchical micromesopores and well-balanced acid sites. These results reveal that the use of bioglycerol along with a typical TPA+ template had a promotional effect on creating such special properties in the Zn-Z-GT material. The Zn-Z-GT catalyst exhibited excellent catalytic performance in the naphtha aromatization reaction, resulting in achieving ∼58 wt % of the aromatic product and useful gas byproduct (14 wt %) with a minimum coke content (∼4 wt %) in a 12 h reaction period ascribed to its combined effect of hierarchical micromesopores and well-balanced acidity with optimum Lewis acid sites. The liquid product possessing high alkyl-aromatics with a high octane value (RON ∼ 109) produced in the present study can be used as an octane booster for liquid gasoline. The high alkyl-aromatics (>50 wt %) content of the liquid product also attracts various petrochemical applications. The effective utilization of waste bioglycerol as a green template and mesopore creator for the preparation of Zn-Z-GT can exhibit sustainability in the resultant material.