No abstract

No abstract

No abstract

Various magnesium oxide catalysts have been prepared by thermal treatment of two different precursors: Mg(OH), and Mg5(OH),(C03),. An additional system based on MgO and doped with B203 was also prepared. The textural and acid-base properties of the catalysts were investigated. The synthesized solids were characterized from adsorption isotherms, X-ray diffraction (XRD), 'H MAS NMR, diffuse reflectance IR Fourier transform spectroscopy (DRIFT) and temperature-programmed desorption-mass spectrometry (TPD-MS) of adsorbed probe molecules (pyridine, 2,6-dimethylpyridine and carbon dioxide). The surface properties of the solids were found to be strongly influenced by the magnesium oxide preparation conditions (uiz. the precursor and calcination method used). Use of Mg(OH), as the precursor and in uucuo calcination provided highly basic solids (those with the highest proportions of strong basic sites). Various types of Lewis-acid sites were observed in the catalysts prepared in uacuo, probably as the result of the presence of Mg2+ cations of low coordination after the calcination.

Several intermediates of the oxidative coupling of areneboronic acids to afford biaryls have been identified by electrospray ionization mass spectrometry. Knowledge has been gained about the steps occurring after the biaryl formation and leading to the recovery of the catalytic species.

Two different catalysts consisting of Pt/TiO2 and Pd/TiO2 were submitted to diverse oxidative and reductive calcination treatments and tested for photocatalytic reforming of glucose water solution (as a model of biomass component) in H2 production. Oxidation and reduction at 850 °C resulted in better photocatalysts for hydrogen production than Degussa P-25 and the ones prepared at 500 °C, despite the fact that the former consisted in very low surface area (6-8 m2/g) rutile titania specimens. The platinum-containing systems prepared at 850 °C give the most effective catalysts. XPS characterization of the systems showed that thermal treatment at 850 °C resulted in electron transfer from titania to metal particles through the so-called strong metal-support interaction (SMSI) effect. Furthermore, the greater the SMSI effect, the better the catalytic performance. Improvement in photocatalytic behavior is explained in terms of avoidance of electron-hole recombination through the electron transfer from titania to metal particles.

No abstract

No abstract