Gábor Schubert - Academia.edu (original) (raw)

Papers by Gábor Schubert

Journal of Comparative Pathology and Therapeutics

Environmental change let it be induced either by climatic or anthropogenic factors has had a key ... more Environmental change let it be induced either by climatic or anthropogenic factors has had a key role in determining the rate of aeolian sediment transfer, on the highly sensitive landscape of the Danube-Tisza Interfluve, Hungary. The study area is located on a former alluvial fan of the Danube, abandoned by the river in the Late Pleistocene, and then reshaped by aeolian activity. The resultant dune fields were time to time reactivated during the Holocene and historical times. As this part of the Carpathian Basin is often stricken by droughts, anthropogenic factors, such as forest clearances and/or overgrazing could easily lead to the disturbance of morphological stability. These effects acted on a local level, however in certain historical periods they supposedly were more extended and general. An era of this type was the time of Turkish occupation (16th-17th c.) and the following two centuries. During the Turkish rule the territory was cleared of forests and became deserted. Follo...

American Journal of Analytical Chemistry, 2014

The photo-induced vapor-phase decomposition of dimethyl ether was investigated on Pt metals depos... more The photo-induced vapor-phase decomposition of dimethyl ether was investigated on Pt metals deposited on pure and N-doped TiO2. Infrared spectroscopic measurements revealed that adsorption of dimethyl ether on TiO2 samples underwent partial dissociation to methoxy species. Illumination of the (CH3)2O-TiO2 and (CH3)2O-M/TiO2 systems led to the conversion of methoxy into adsorbed formate. In the case of metal-promoted TiO2 catalysts, CO bonded to the metals was also detected. Pure titania exhibited a very little photoactivity. Deposition of Pt metals on TiO2 markedly enhanced the extent of photocatalytic decomposition of dimethyl ether to give H2 and CO2 as the major products. A small amount of CO and methyl formate was also identified in the products. The most active metal was the Rh followed by Pd, Ir, Pt and Ru. When the bandgap of TiO2 was lowered by N-doping, the photocatalytic activity of metal/TiO2 catalysts appreciably increased. The effect of metals was explained by a better separation of charge carriers induced by illumination and by enhanced electronic interaction between metal nanoparticles and TiO2.

The Journal of Physical Chemistry C, 2012

The photoinduced vapor-phase decomposition of formic acid was investigated on pure, N-doped and m... more The photoinduced vapor-phase decomposition of formic acid was investigated on pure, N-doped and metal-promoted TiO 2. The catalysts were characterized by bandgap determination, and by Fourier transformed infrared spectroscopy, the bandgap of N-doped TiO 2 was narrowed by 0.5−1.02 eV. IR studies revealed that illumination of the HCOOH−TiO 2 system initiated the decomposition of adsorbed formate species. On the IR spectra of metal-promoted TiO 2 adsorbed CO attached to the metals was also detected. The photodecomposition of formic acid on pure TiO 2 occurs to only a limited extent to yield H 2 and CO 2 as the major products with a small amount of CO. Depending on the origin of TiO 2 and on the preparation, N-doped TiO 2 exhibited higher activity. Its efficiency is increased with the narrowing of the bandgap, a feature attributed to the prevention of electron−hole recombination. The deposition of noble metals on pure and N-modified TiO 2 dramatically enhanced the extent of photodecomposition of formic acid. Pd/TiO 2 was found to be the most active catalyst. Addition of water to formic acid completely eliminated the small amount of CO formed. Both the N-doped TiO 2 and metal-promoted TiO 2 + N samples exhibited photocatalytic effects even in visible light. The promoting effect of metals was explained by a better separation of charge carriers induced by illumination and by improved electronic communication between metal particles and TiO 2 .

The Journal of Physical Chemistry C, 2013

The photoinduced vapor-phase decomposition of methyl formate was investigated on pure and on Pt-m... more The photoinduced vapor-phase decomposition of methyl formate was investigated on pure and on Pt-metals-promoted TiO 2. Infrared spectroscopic studies revealed that illumination induced the dissociation of molecularly adsorbed methyl formate to formate on pure TiO 2 even at ∼186 K. This process is indicated by the appearance of the absorption band at 1580−1590 cm −1 due to asymmetric stretch of formate species. The extent of the dissociation is increased with the time of irradiation. Deposition of Pt metals on TiO 2 only slightly influenced this process. The photocatalytic decomposition of methyl formate vapor on pure TiO 2 occurred to only a limited extent at 300 K, but the deposition of Pt metals on TiO 2 appreciably enhanced the extent and the rate of photodecomposition. Nevertheless the photocatalytic reaction of methyl formate proceeded more slowly compared to that of formic acid on the same catalysts, and produced more CO. Addition of H 2 O to the methyl formate decreased the CO/H 2 ratio by a factor of 4. When the bandgap of TiO 2 support was lowered by N-doping from 3.02 to 1.98 eV, the photocatalytic activity of metal/TiO 2 catalysts appreciably increased, and the decomposition of methyl formate was observed even in visible light.

Journal of Photochemistry and Photobiology A: Chemistry, 2013

The effects of Au particles of different sizes were investigated on the photocatalytic decomposit... more The effects of Au particles of different sizes were investigated on the photocatalytic decompositions of methanol and ethanol on pure or N-doped TiO 2. IR studies revealed that the deposition of Au promoted the dissociation of both compounds during illumination and also resulted in the formation of formate species. Whereas the photo-induced decompositions of methanol and ethanol occurred to only a limited extent on pure TiO 2 , the deposition of Au, particularly as nanosized particles, markedly enhanced the rate and the extent of the photocatalyzed reactions. An interesting feature of the photodecomposition of methanol was that, besides H 2 , CO 2 and CO, a significant amount of methyl formate was also produced. Addition of H 2 O or O 2 to the alcohol in both cases decreased the level of CO formed, and in the case of methanol CO was completely eliminated. Au particles on N-doped TiO 2 with a lower bandgap catalyzed the photodecompositions of both compounds even in visible light.

Journal of Catalysis, 2014

The photocatalytic vapor-phase decomposition and oxidation of dimethyl ether were investigated on... more The photocatalytic vapor-phase decomposition and oxidation of dimethyl ether were investigated on pure and Au-promoted TiO 2. Infrared spectroscopic studies revealed that dimethyl ether adsorbed on TiO 2-based catalysts undergoes partial dissociation to methoxy. Illumination induced a surface reaction and led to the formation of formate species. Whereas pure TiO 2 exhibited only a slight photoactivity, the deposition of Au on TiO 2 significantly enhanced the extent of the photocatalytic decomposition to yield H 2 and CO 2 with a small amount of CO. Addition of H 2 O increased the extent of photocatalytic decomposition and eliminated the CO formed. A very high catalytic effect of Au/TiO 2 was observed in the photocatalytic oxidation of dimethyl ether to produce H 2 free of CO. When the bandgap of the TiO 2 support was lowered by N-doping from 3.02 eV to 1.98 eV, the photocatalytic decomposition and oxidation of dimethyl ether were observed even in visible light.

International Journal of Hydrogen Energy, 2013

The photo-induced vapor-phase decompositions of formic acid and methyl formate were investigated ... more The photo-induced vapor-phase decompositions of formic acid and methyl formate were investigated on pure, N-doped and Au-promoted TiO 2. Infrared (IR) spectroscopic studies revealed that illumination initiated the decomposition of adsorbed formate formed in the dissociation of formic acid and located mainly on TiO 2. The photocatalytic decompositions of formic acid and methyl formate vapor on pure TiO 2 occurred to only a limited extent. The deposition of Au on pure or doped TiO 2 markedly enhanced the extent of photocatalytic decomposition of formic acid. The main process was dehydrogenation to give H 2 and CO 2. The formation of CO occurred to only a very small extent. Addition of O 2 or H 2 O to the formic acid decreased the CO level from w0.8% to w0.088%. Similar features were experienced in the photocatalytic decomposition of methyl formate, which dissociated in part to give surface formate. Experiments over Au deposited on N-doped TiO 2 revealed that the photo-induced decomposition of both compounds occurs even in visible light.

Catalysis Letters, 2012

The photo-induced vapor-phase decomposition of formic acid was investigated on pure, N-doped and ... more The photo-induced vapor-phase decomposition of formic acid was investigated on pure, N-doped and Rh-promoted TiO 2. The bandgap of TiO 2 was narrowed by 0.82-1.04 eV as a result of the incorporation N into TiO 2. Adsorption of formic acid on pure TiO 2 produced strong absorption bands due to formate species, the intensity of which decreased by illumination. The photodecomposition of formic acid on pure TiO 2 at 300 K occurs to only a limited extent: on N-doped TiO 2 , however, it is enhanced by a factor of 2-4. The N-modified TiO 2 catalyzes the photoreaction even in the visible light, which is attributed to the prevention of electron-hole recombination. The deposition of Rh on TiO 2 markedly increased the extent of photodecomposition. The conversion is complete in 200 min, while the extent of decomposition reaches only *30% on pure TiO 2. The effect of Rh is explained by a better separation of charge carriers induced by illumination and by enhanced electron donation to the adsorbed formate species. On TiO 2 samples both the dehydrogenation and dehydration reactions occurred, on Rh/TiO 2 only a trace amount of CO was formed. Addition of water to formic acid eliminated this CO, but exerted no other influence on the occurrence the photoreaction.

Journal of Catalysis, 2012

The photo-induced vapor-phase reaction of methanol was investigated on Pt metals deposited on pur... more The photo-induced vapor-phase reaction of methanol was investigated on Pt metals deposited on pure and N-doped TiO 2. Infrared spectroscopic measurements revealed that illumination of the CH 3 OH-TiO 2 and CH 3 OH-M/TiO 2 systems led to the conversion of adsorbed methoxy species into adsorbed formate. In the case of metal-promoted TiO 2 catalysts CO bonded to the metals was also detected. Pure titania exhibited very little photoactivity, its efficiency, however, increased with the narrowing of its bandgap by N-doping, a feature attributed to the prevention of electron-hole recombination. Deposition of Pt metals on pure and N-doped TiO 2 dramatically enhanced the extent of photoreaction of methanol even in visible light: hydrogen and methyl formate with selectivities of 83-90% were the major products. The most active metal was Pt followed by Pd, Ir, Rh, and Ru. The effect of metal was explained by a better separation of charge carriers induced by illumination and by enhanced electronic interaction between metal nanoparticles and TiO 2 .

Inorganica Chimica Acta, 2006

The biomimetic dioximatoiron complexes [Fe(Hdmed)] + and [Fe(H 2 dmdt)] 2+ act as catecholase mod... more The biomimetic dioximatoiron complexes [Fe(Hdmed)] + and [Fe(H 2 dmdt)] 2+ act as catecholase models but the latter also catalyzes the intradiol cleavage of 3,5-ditert-butylcatechol. This remarkable selectivity was ascribed to the stable, hydrogen-bonded, macrocyclic coordination sphere of [Fe(Hdmed)] + , precluding bidentate catechol binding, as opposed to the less stable, mobile structure of [Fe(H 2 dmdt)] 2+ . This hypothesis is supported by the structures of [Fe(Hdmed)] + and [Fe(H 2 dmdt)] 2+ determined by X-ray diffraction in 1 M methanol solution. This study is a demonstrative example for the capabilities of the X-ray diffraction technique applied for complexes in the solution phase. The characteristic bond lengths of the complex and the number of solvent molecules in the solvation shell have been determined. To examine the structure of the complexes, gas phase density functional geometry optimizations were performed by using the ADF-2004.01 and packages. The PCM methodology was applied to estimate the effect of solvent on the relative energetics of the low-spin and high-spin electronic states of the complexes. The calculations confirmed that the electronic ground state corresponds to the triplet state for both complexes.