title: In Situ Solid-State (13)C NMR Observation of Pore Mouth Catalysis in Etherification of β-Citronellene with Ethanol on Zeolite Beta.
abstract: The reaction mechanism of etherification of β-citronellene with ethanol in liquid phase over acid zeolite beta is revealed by in situ solid-state (13)C NMR spectroscopy. Comparison of (13)C Hahn-echo and (1)H-(13)C cross-polarization NMR characteristics is used to discriminate between molecules freely moving in liquid phase outside the zeolite and molecules adsorbed inside zeolite pores and in pore mouths. In the absence of ethanol, β-citronellene molecules enter zeolite pores and react to isomers. In the presence of ethanol, the concentration of β-citronellene inside zeolite pores is very low because of preferential adsorption of ethanol. The etherification reaction proceeds by adsorption of β-citronellene molecule from the external liquid phase in a pore opening where it reacts with ethanol from inside the pore. By competitive adsorption, ethanol prevents the undesired side reaction of β-citronellene isomerization inside zeolite pores. β-citronellene etherification on zeolite beta is suppressed by bulky base molecules (2,4,6-collidine and 2,6-ditertiarybutylpyridine) that do not enter the zeolite pores confirming the involvement of easily accessible acid sites in pore openings. The use of in situ solid-state NMR to probe the transition from intracrystalline catalysis to pore mouth catalysis depending on reaction conditions is demonstrated for the first time. The study further highlights the potential of this NMR approach for investigations of adsorption of multicomponent mixtures in general.
authors: Centre for Surface Chemistry and Catalysis, KU Leuven , Celestijnenlaan 200F, Box 2461, 3001 Heverlee, Leuven, Belgium.
authors: Sambhu
authors: S
authors: Radhakrishnan
authors: Centre for Surface Chemistry and Catalysis, KU Leuven , Celestijnenlaan 200F, Box 2461, 3001 Heverlee, Leuven, Belgium.
authors: Pieter-Jan
authors: PJ
authors: Goossens
authors: Centre for Surface Chemistry and Catalysis, KU Leuven , Celestijnenlaan 200F, Box 2461, 3001 Heverlee, Leuven, Belgium.
authors: Pieter C M M
authors: PC
authors: Magusin
authors: Centre for Surface Chemistry and Catalysis, KU Leuven , Celestijnenlaan 200F, Box 2461, 3001 Heverlee, Leuven, Belgium.
authors: Sreeprasanth Pulinthanathu
authors: SP
authors: Sree
authors: Department of Solid State Sciences, CoCooN, Ghent University , Krijgslaan 281 (S1), Ghent 9000, Belgium.
authors: Christophe
authors: C
authors: Detavernier
authors: Centre for Surface Chemistry and Catalysis, KU Leuven , Celestijnenlaan 200F, Box 2461, 3001 Heverlee, Leuven, Belgium.
authors: Eric
authors: E
authors: Breynaert
authors: Tectospin, Institut Lavoisier, UMR 8180, Université de Versailles st. Quentin en Yvelines , 45 Avenue des Etats Unis, 78035 Versailles, Cedex, France.|CEMHTI, CNRS UPR 3079 , 1D Avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France.
authors: Charlotte
authors: C
authors: Martineau
authors: Centre for Surface Chemistry and Catalysis, KU Leuven , Celestijnenlaan 200F, Box 2461, 3001 Heverlee, Leuven, Belgium.|Tectospin, Institut Lavoisier, UMR 8180, Université de Versailles st. Quentin en Yvelines , 45 Avenue des Etats Unis, 78035 Versailles, Cedex, France.
authors: Francis
authors: F
authors: Taulelle
authors: Centre for Surface Chemistry and Catalysis, KU Leuven , Celestijnenlaan 200F, Box 2461, 3001 Heverlee, Leuven, Belgium.
authors: Johan A
authors: JA
authors: Martens