NaOH modified WO3/SiO2 catalysts for propylene production from 2‐butene and ethylene metathesis

Chinese Journal of Catalysis 35 (2014) 232–241
NaOH modified WO3/SiO2 catalysts for propylene production from 2‐butene and ethylene metathesis
Surasa Maksasithorn  (a), Damien P. Debecker  (b), Piyasan Praserthdam  (a), Joongjai Panpranot  (a),
Kongkiat Suriye  (c), Sirachaya Kunjara Na Ayudhya  (c)
a Center of Excellence on Catalysis and Catalytic Reaction Engineering, Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn
University, Bangkok 10330, Thailand
b Institute of Condensed Matter and Nanoscience – Molecules, Solids and Reactivity (IMCN/MOST), Université catholique de Louvain, Croix du Sud 2/17,
1348 Louvain‐La‐Neuve, Belgium
c SCG Chemicals, Co., Ltd., 1 Siam Cement Road, Bangsue, Bangkok 10800, Thailand
Abstract
A WO3/SiO2 catalyst is used in industry to produce propylene from 2‐butene and ethylene metathesis. Catalysts with various WO3 loading (4% to 10%) were prepared by impregnation and tested for the metathesis of ethene and trans‐2‐butene. Ion exchange of NaOH onto the WO3/SiO2 catalyst was used to mitigate the acidity of the catalysts in a controlled way. At low WO3 loading, the treatment with large amounts of NaOH resulted in a significant decrease in metathesis activity concomitant with significant W leaching and marked structural changes (XRD, Raman). At higher WO3 loading (6% to 10%), the treatment with NaOH mainly resulted in a decrease in acidity. FT‐IR experiments after adsorption of pyridine showed that the Lewis acidic sites were poisoned by sodium. Nevertheless, the metathesis activity remained constant after the NaOH treatment. This suggested that the remaining acidity on the catalyst was enough to ensure the efficient formation of the carbene active sites. Interestingly, Na poisoning resulted in some modification of the selectivity. The mitigation of acidity was shown to favor propene selectivity over the formation of isomerization products (cis‐2‐butene, 1‐butene, etc.). Moreover, treatment with NaOH led to a shorter induction period and reduced coke formation on the WO3/SiO2 catalyst.
In the present study, researchers tested WO3/SiO2 catalysts that have different loading under conditions close to the industrial ones to evaluate the impact of Na poisoning. Infrared spectroscopy of pyridine adsorption was used to evaluate the impact of Brönsted and Lewis sites on metathesis activity. Authors discuss the effect of Na poisoning on the undesired side reactions, catalyst stability, and coke formation.
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