The influence of Si/Al ratio on the distribution of OH groups in zeolites with MWW topology

A series of MWW-type zeolites of increasing Si/Al ratio were investigated with respect to their acidic properties. Concentration of the Brønsted acid centers located at the external crystal surface was invariant for the entire series. Ethanol conversion to ethyl-tert-butyl ether, proceeding only at the external surface, was also constant. The OH groups in MWW zeolites were found to be homogeneous with proton affinity value equal to 1142.7 kJ/mol

Carbon nanotubes, silica and titania supported heteropolyacid H3PW12O40H_{3}PW_{12}O_{40} as the catalyst for ethanol conversion

The new catalyst: heteropolyacid H 3 PW 12 O 40 (HPA) supported on carbon nanotubes (CNTs) for ethanol conversion was compared with silica and titania supported heteropolyacid. The ethanol conversion did not depend on the type of the support up to reaction temperature 403 K while above 423 K ethanol conversion was higher for HPA on CNTs than for unsupported HPA. Generally, the most active catalysts were obtained by using high surface area silica as the support

Ethanol conversion over cesium-doped mono- and bi-cationic aluminum and gallium H3PW12O40H_3PW_{12}O_{40} salts

The objective of this study was synthesis, characterization, and catalytic testing of mono-cationic (GaPW12O40, AlPW12O40) and bi-cationic (CsGa0.5H0.5PW12O40, CsAl0.5H0.5PW12O40) salts of tungstophosphoric acid. These heteropoly salts are characterized by Brönsted acidity derived from protons generated by dissociation of water molecules coordinated to the metal atoms. Catalytic activity of the studied salts was evaluated based on ethanol conversion and compared with the well-known parent heteropolyacid H3PW12O40. The reaction products, ethylene and diethyl ether, were monitored simultaneously by FTIR spectroscopy and chromatographic analysis. The infra-red studies indicated that ethylene is formed not only from ethanol but also by diethyl ether decomposition. Cs-doped bi-cationic catalysts exhibited higher activity for ethylene and ether formation than the mono-cationic salts. The following order of catalytic activity was established: H3PW12O40 > CsGa0.5H0.5PW12O40 ∼ CsAl0.5H0.5PW12O40 > GaPW12O40 > AlPW12O40. It is in agreement with the order of their acid strength determined by microcalorimetry and specific surface areas of the studied catalysts