title: Effect of preparation method and CuO promotion in the conversion of ethanol into 1,3-butadiene over SiO₂-MgO catalysts.
abstract: Silica-magnesia (Si/Mg=1:1) catalysts were studied in the one-pot conversion of ethanol to butadiene. The catalyst synthesis method was found to greatly influence morphology and performance, with materials prepared through wet-kneading performing best both in terms of ethanol conversion and butadiene yield. Detailed characterization of the catalysts synthesized through co-precipitation or wet-kneading allowed correlation of activity and selectivity with morphology, textural properties, crystallinity, and acidity/basicity. The higher yields achieved with the wet-kneaded catalysts were attributed to a morphology consisting of SiO2 spheres embedded in a thin layer of MgO. The particle size of the SiO2 catalysts also influenced performance, with catalysts with smaller SiO2 spheres showing higher activity. Temperature-programmed desorption (TPD) measurements showed that best butadiene yields were obtained with SiO2-MgO catalysts characterized by an intermediate amount of acidic and basic sites. A Hammett indicator study showed the catalysts' pK(a) value to be inversely correlated with the amount of dehydration by-products formed. Butadiene yields could be further improved by the addition of 1 wt% of CuO as promoter to give butadiene yields and selectivities as high as 40% and 53%, respectively. The copper promoter boosts the production of the acetaldehyde intermediate changing the rate-determining step of the process. TEM-energy-dispersive X-ray (EDX) analyses showed CuO to be present on both the SiO2 and MgO components. UV/Vis spectra of promoted catalysts in turn pointed at the presence of cluster-like CuO species, which are proposed to be responsible for the increased butadiene production.
authors.affiliation: Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (The Netherlands).
authors.forename: Carlo
authors.initials: C
authors.lastname: Angelici
authors.forename: Marjolein E Z
authors.initials: ME
authors.lastname: Velthoen
authors.forename: Bert M
authors.initials: BM
authors.lastname: Weckhuysen
authors.forename: Pieter C A
authors.initials: PC
authors.lastname: Bruijnincx
mesh_terms: D002070:Butadienes / Q000737:chemistry*; D002384:Catalysis; D003300:Copper / Q000737:chemistry*; D000431:Ethanol / Q000737:chemistry*; D008277:Magnesium Oxide / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D002070:Butadienes; D008277:Magnesium Oxide; D000431:Ethanol; D012822:Silicon Dioxide; D003300:Copper; C031763:1,3-butadiene; C030973:cupric oxide
keywords: butadiene; copper; ethanol; heterogeneous catalysis; silica-magnesia