The environmental impact of potassium tungstophosphate/ZSM-5 zeolite: Insight into catalysis and adsorption processes

Abstract

Environmental implementation of novel composite materials comprising potassium tungstophosphate (KPW) and ZSM-5 zeolite was tested in ethene production and pesticide removal. The study revealed that the binding of KPW to ZSM-5 zeolites of different Si/Al ratios affects the formation of active centres for catalytic and adsorption processes. Brønsted active sites present in the zeolite framework are synergistically joined with Lewis centres and additional Brønsted centres through the impregnation of potassium tungstophosphate, which resulted in improvement of stability and activity of investigated materials. Adsorption and catalytic performance were found to be influenced by the order of addition of salt precursors and by post-synthesis thermal treatment. The best results found both in ethanol dehydration and nicosulfuron removal were for the same sample of KPW supported at zeolite ZSM-5 (SiO2/Al2O3 = 30). The prominent ethanol conversion of 98% and the highest and most stable selectivity toward ethene were evidenced, along with the capacity of 28.4 mg of targeted pesticide retained per gram of designed KPW/ZSM composite. This comprehensive investigation enabled insight into active site formations in the efficient KPW/ZSM composites. Different approaches to implementation revealed that a lower Si/Al ratio in zeolite promotes efficient K+ exchange, which combined with two-phased in situ preparation of KPW as active phase, evidently leads to the formation of isolated sites of superior activity for both catalytic and adsorptive procedures.