Dr. Sotiria Mostrou

Au/TiO2 is a much-used catalyst for the conversion of ethanol
to acetic acid. The proposed mechanism speaks of two essential
reaction steps on the catalytic surface. The first is the ethanol to
acetaldehyde and the second the acetaldehyde to acetic acid. When
operating in the gas phase, acetic acid is usually absent. This work
focuses on determining what triggers the second step by comparing
the ethanol with acetaldehyde oxidation and the liquid with gas-phase
reaction. We… Mehr anzeigen

Au/TiO2 is a much-used catalyst for the conversion of ethanol
to acetic acid. The proposed mechanism speaks of two essential
reaction steps on the catalytic surface. The first is the ethanol to
acetaldehyde and the second the acetaldehyde to acetic acid. When
operating in the gas phase, acetic acid is usually absent. This work
focuses on determining what triggers the second step by comparing
the ethanol with acetaldehyde oxidation and the liquid with gas-phase
reaction. We propose an updated reaction mechanism: acetaldehyde
autoxidises non-catalytically to acetic acid, likely driven by radicals.
The requirement for the autoxidation is the presence of oxygen and
water in the liquid-phase. The understanding of the interplay between
the catalytic ethanol to acetaldehyde and the following non-catalytic
reaction step provides guiding principles for the design of new and
more selective alcohol oxidation catalysts. Weniger anzeigen

The solar thermochemical water and carbon dioxide splitting, mediated by ceria, has a great potential to produce “green” syngas. Chromium was added to ceria to improve the syngas production. Three preparation methods were applied, resulting in different morphologies allowing to investigate the role of chromium. The samples were characterized by X‐ray diffraction, Raman and X-ray spectroscopy, and electron microscopy. Materials made by polymerized-complex-method and dry-impregnation consisted of… Mehr anzeigen

The solar thermochemical water and carbon dioxide splitting, mediated by ceria, has a great potential to produce “green” syngas. Chromium was added to ceria to improve the syngas production. Three preparation methods were applied, resulting in different morphologies allowing to investigate the role of chromium. The samples were characterized by X‐ray diffraction, Raman and X-ray spectroscopy, and electron microscopy. Materials made by polymerized-complex-method and dry-impregnation consisted of two crystal phases: ceria and chromia. In contrast, materials made by flame-spray pyrolysis exhibited a homogeneous Cr-doped ceria phase, and chromia was found only at a chromium-content higher than 25 mol%. The chromium-doped ceria released additional oxygen during the formation of CeCrO3 perovskite, which did not enhance hydrogen or carbon monoxide production. All chromia-containing samples exhibited improved oxygen exchange capacity, possibly due to a redox cycle of chromia itself, and significantly improved the activity of water and carbon dioxide splitting. Hydrogen production increased from 3.2 to 6.7 mL/g and the time to reach redox equilibrium was shorten from 41 to 3 min. The best hydrogen and carbon dioxide production rates were up to 20 and 500 times higher than pure ceria, respectively. The presence of chromium is therefore crucial as a catalyst, promoter, and oxygen storage enhancer. This work emphasises the importance of a catalysed re‐oxidation reaction and demonstrates that a metal oxide, becoming active in situ, can catalyse water and carbon dioxide splitting. Weniger anzeigen

The heterogeneously catalyzed oxidation of bioethanol offers a promising route to bio-based acetic acid. Here, we assess an alternative method to support gold nanoparticles, which aims to improve selectivity to acetic acid through minimizing over-oxidation to carbon dioxide. The most promising support system is 5 wt % titanium on silica, which combines the high surface area of silica with the stabilizing effect of titania on the gold particles. Compared to gold–silica systems, which require a… Mehr anzeigen

The heterogeneously catalyzed oxidation of bioethanol offers a promising route to bio-based acetic acid. Here, we assess an alternative method to support gold nanoparticles, which aims to improve selectivity to acetic acid through minimizing over-oxidation to carbon dioxide. The most promising support system is 5 wt % titanium on silica, which combines the high surface area of silica with the stabilizing effect of titania on the gold particles. Compared to gold–silica systems, which require a complex synthesis method, small quantities of titanium promoted the formation of gold nanoparticles during a simple deposition–precipitation. Characterization of the catalyst with X-ray absorption spectroscopy shows that titanium is highly dispersed in the form of small, possibly dimeric, titanium(IV) structures, which are isolated and stabilize gold nanoparticles, possibly minimizing sintering effects during synthesis. The size of the gold particles depends on the pre-treatment of the titanium–silica support before gold deposition, with larger titanium structures hosting larger gold particles. Acetic acid yield over the titanium–silica-supported gold systems improved by about 1.6 times, compared to pure titania-supported gold. The high activity of those catalysts suggests that bulk, crystalline titania is not required for the reaction, encouraging the use of mixed supports to combine their benefits. Those support systems, besides improving selectivity, offer high surface area and a low-cost filler material, which brings ethanol oxidation one step further to the industry. Additionally, the low loading of titanium permits studying the reaction mechanisms on the gold–titanium interface with bulk characterization techniques. Weniger anzeigen

The heterogeneously catalyzed oxidation of bioethanol offers a promising route to bio-based acetic acid. Here, we assess an alternative method to support gold nanoparticles, which aims to improve selectivity to acetic acid through minimizing over-oxidation to carbon dioxide. The most promising support system is 5 wt % titanium on silica, which combines the high surface area of silica with the stabilizing effect of titania on the gold particles. Compared to gold–silica systems, which require a… Mehr anzeigen

The heterogeneously catalyzed oxidation of bioethanol offers a promising route to bio-based acetic acid. Here, we assess an alternative method to support gold nanoparticles, which aims to improve selectivity to acetic acid through minimizing over-oxidation to carbon dioxide. The most promising support system is 5 wt % titanium on silica, which combines the high surface area of silica with the stabilizing effect of titania on the gold particles. Compared to gold–silica systems, which require a complex synthesis method, small quantities of titanium promoted the formation of gold nanoparticles during a simple deposition–precipitation. Characterization of the catalyst with X-ray absorption spectroscopy shows that titanium is highly dispersed in the form of small, possibly dimeric, titanium(IV) structures, which are isolated and stabilize gold nanoparticles, possibly minimizing sintering effects during synthesis. The size of the gold particles depends on the pre-treatment of the titanium–silica support before gold deposition, with larger titanium structures hosting larger gold particles. Acetic acid yield over the titanium–silica-supported gold systems improved by about 1.6 times, compared to pure titania-supported gold. The high activity of those catalysts suggests that bulk, crystalline titania is not required for the reaction, encouraging the use of mixed supports to combine their benefits. Those support systems, besides improving selectivity, offer high surface area and a low-cost filler material, which brings ethanol oxidation one step further to the industry. Additionally, the low loading of titanium permits studying the reaction mechanisms on the gold–titanium interface with bulk characterization techniques. Weniger anzeigen