The epoxidation of propene over gold nanoparticle catalysts

Different gold nanoparticle catalysts on titania, silica, and titanosilicate supports are compared in the hydro-epoxidation of propene. All catalysts tested were active in the propene epoxidation, with Au/TiO2 showing the highest activity at low temperature, but also a high rate of deactivation. It is shown that the deactivation of the catalysts is directly related to a side reaction of a bidentate propoxy reaction intermediate. This species can react to produce propene oxide, but as a side reaction it can also produce very strongly adsorbed species, most likely carbonates, which cause a reversible deactivation. There are no indications that the catalyst deactivation is caused by changes in the size or the state of the gold nanoparticles. Catalysts containing a lower amount of titania dispersed in or on a silica support are more stable, but require a higher reaction temperature for a similar activity. Ti-SBA-15 is the most promising support material, but the gold deposition inside the structure requires further optimization. A key factor, that needs to be solved for all gold catalysts, is the efficiency in which hydrogen is used as a coreactant. The currently obtained hydrogen efficiencies of up to 10% are insufficient to run a process profitably

Synthesis and characterization of Au/Ti-SBA-15 catalysts for the vapour phase epoxidation of propylene

Au-Ti-SBA-15 catalysts have been synthesized using different preparation routes. Ti-SBA-15 supports with Si/Ti ratio ranging from 10 to 80 have been prepared by grafting and direct synthesis. X-ray fluorescence (XRF), X-ray diffraction (XRD), diffuse reflectance UV-visible spectroscopy (DRS), transmission electron microscopy (TEM) and nitrogen sorption were applied for the characterization of the prepared catalysts. The catalytic activities of the Au/Ti-SBA-15 materials have been investigated in the direct epoxidation of propene by using a mixture of H2 and O2 and its performance was compared with an Au/TiO2 catalyst. The activity results were then interpreted with reference to the characterization

Synthesis and characterization of Au/Ti-SBA-15 catalysts for the vapour phase epoxidation of propylene

Au-Ti-SBA-15 catalysts have been synthesized using different preparation routes. Ti-SBA-15 supports with Si/Ti ratio ranging from 10 to 80 have been prepared by grafting and direct synthesis. X-ray fluorescence (XRF), X-ray diffraction (XRD), diffuse reflectance UV-visible spectroscopy (DRS), transmission electron microscopy (TEM) and nitrogen sorption were applied for the characterization of the prepared catalysts. The catalytic activities of the Au/Ti-SBA-15 materials have been investigated in the direct epoxidation of propene by using a mixture of H2 and O2 and its performance was compared with an Au/TiO2 catalyst. The activity results were then interpreted with reference to the characterization

A transient kinetic analysis of the epoxidation of propene over gold-titania catalysts

Abstract onl

Propene epoxidation over Au/Ti-SBA-15 catalysts

Highly dispersed gold nanoparticles were synthesized within the channels of a mesoporous Ti-SBA-15 support, followed by thorough catalyst characterization and testing in the selective epoxidation of propene to propene oxide. For this purpose, two series of Ti-SBA-15 materials differing in their Ti content were prepared by either grafting or direct synthesis. The resulting Au/Ti-SBA-15 catalyst materials were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen sorption, UV–visible diffuse reflectance spectroscopy (UV–vis DRS), and X-ray absorption spectroscopy (EXAFS and XANES) at both the Ti K and Au L3 edges. The catalytic performance of the Au/Ti-SBA-15 materials was been evaluated in the direct epoxidation of propene using a mixture of H2 and O2. The reaction data indicate that Au/Ti-SBA-15 materials obtained by Ti grafting have greater catalytic activity than the samples in which Ti-SBA-15 was obtained by direct synthesis. These differences in catalytic behavior are attributed to differences in the amount and dispersion of Ti within the mesoporous silica support, as well as to differences in the Au nanoparticle size, and are discussed in relation to data obtained previously for Au/TiO2 catalysts

Photocatalytic decomposition of acetone over dc-magnetron sputtering supported vanadia/TiO2 catalysts

Two series of titania-based photocatalysts were prepared by the sputtering method, in pure Ar atmosphere at a pressure of 0.5 Pa using a vanadium target source in a direct dc mode with a discharge of 300 V. The time of deposition was varied between 1 and 10 min in order to obtain different thickness of vanadium films. The first catalysts series (samples V/TiO2(A)-n) was prepared deposing vanadium Oil pure TiO2 anatase, while for the second series (samples V/TiO2(AR)-n) the deposition was made onto TiO2 Degussa P25. The samples have been investigated by means of vibrational (DRIFT and Raman) and optical (UV-vis in the DRS mode). Chemical analysis of the samples was made using the ICP-AES technique, while the crystalline structure of the deposed films onto the TiO2 supports was checked by X-ray diffraction (XRD). The samples morphology was analyzed using the AFM microscopy. The photocatalytic decomposition of acetone was considered as a reaction test. The activity of the investigated catalysts was found to be influenced by both the amount of vanadium and the Support nature. Among the investigated catalysts V/TiO2(AR)-32 nm exhibited the higher activity. The activity of this catalyst was also superior to that of TiO2 Degussa P25. (C) 2008 Elsevier B.V. All rights reserved

Understanding the effect of postsynthesis ammonium treatment on the catalytic activity of Au/TI-SBA-15 catalysts for the oxidation of propene

Postsynthesis ammonium treatment induces a substantial increase in the catalytic activity of Au/Ti-SBA-15 catalysts for the direct vapor-phase epoxidation of propylene using hydrogen and oxygen. The PO formation rate of a calcined Au/Ti-SBA-15 catalyst prepared by this method increased from 4.3 mgPO h-1 g-1cat to 37.2 mgPO h-1 g-1cat at 200 °C compared with a catalyst prepared in an identical manner without this treatment. The catalysts were characterized by XRD, N2-sorption, UV–vis–NIR DRS, 29Si MAS NMR, FT-IR spectroscopy, and TEM to gain insight into the relationship between ammonia treatment and catalyst activity. 29Si MAS NMR measurements proved that the ammonium nitrate solution caused hydrolysis of SiOSi or TiOSi bonds, resulting in a Ti-SBA-15 surface with a greater amount of surface hydroxyl groups. FT-IR measurements indicated the presence of amine species that favor the homogeneous deposition of Au nanoparticles. This was confirmed by TEM measurements showing greater metal dispersion for NH4NO3-treated Au/Ti-SBA-15 materials

Synthesis and characterization of Au/Ti-SBA-15 catalysts for the vapour phase epoxidation of propylene

Au-Ti-SBA-15 catalysts have been synthesized using different preparation routes. Ti-SBA-15 supports with Si/Ti ratio ranging from 10 to 80 have been prepared by grafting and direct synthesis. X-ray fluorescence (XRF), X-ray diffraction (XRD), diffuse reflectance UV-visible spectroscopy (DRS), transmission electron microscopy (TEM) and nitrogen sorption were applied for the characterization of the prepared catalysts. The catalytic activities of the Au/Ti-SBA-15 materials have been investigated in the direct epoxidation of propene by using a mixture of H2 and O2 and its performance was compared with an Au/TiO2 catalyst. The activity results were then interpreted with reference to the characterization