Impact of Brønsted acid sites in MWW zeolites modified with cesium and amine species on Knoevenagel condensation

• Published in: Microporous and mesoporous materials 2019-05, Vol.280, p.288-296
• Main Authors: Wojtaszek-Gurdak, Anna, Calvino-Casilda, Vanesa, Grzesinska, Aneta, Martin-Aranda, Rosa, Ziolek, Maria
• Format: Article
• Language: English
• Subjects: Acidity; Basicity; Knoevenagel reactions; Modification with APTMS and Cs; MWW zeolites
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2019.02.007

Layered zeolites of MWW family, MCM-22 and pillared MCM-36, were used as supports for base modifiers: cesium species (introduced via cation exchange or impregnation) and 3-aminopropyl trimethoxysilane (AP). The obtained materials were characterized by different methods (ICP-OES, N2 adsorption, XRD, XPS, TG/DTA, FTIR combined with pyridine adsorption, 2-propanol decomposition) for evaluation of chemical, structural and surface properties. All materials obtained were subjected to the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate and ethyl acetoacetate. The effect of the zeolite structure, the stability of the catalysts as well as acid-base properties of zeolites on the activity in Knoevenagel condensation were considered. Of particular interest was the role of Brønsted acid sites (BAS). The nature of basic sites and BAS played different roles depending on the methylene compound used in the Knoevenagel condensation. AP-modified zeolites were the most active in the condensation between benzaldehyde and ethyl cyanoacetate, in which, in the first step of the reaction AP abstracted hydrogen from methylene carbon in ethyl cyanoacetate. A different reaction pathway was postulated for the condensation with ethyl acetoacetate on the basis of the highest activity of unmodified zeolites and the relationship between benzaldehyde conversion and the number of BAS. For this reaction protonation of benzaldehyde was postulated as the initial step of the reaction. [Display omitted] •Bifunctional catalysts result from modification of MWW zeolites with AP or Cs.•Zeolite BAS enhance benzaldehyde conversion in the reaction with ethyl acetoacetate.•Separation of active centers in AP/MCM-36 decreases selectivity to the main product.•Zeolite BAS adsorb ethyl cyanoacetate and decrease condensation with benzaldehyde.