The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Elias Klemm - One of the best experts on this subject based on the ideXlab platform.
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Multicomponent diffusion and sorption analysis of the direct hydroxylation of methyl-aromatics on zeolites
Recent Advances in the Science and Technology of Zeolites and Related Materials Part B Proceedings of the 14th International Zeolite Conference, 2004Co-Authors: M. Köstner, Elias Klemm, Gerhard EmigAbstract:Abstract We evaluated the impact of multicomponent diffusion and sorption phenomena on the selectivity of the direct hydroxylation of methyl-aromatics, e.g. toluene on HZSM-5. As products the corresponding methyl-phenols, e.g. the three Cresol isomers are formed. To this end, we determined multicomponent diffusion coefficients and sorption isotherms of reactants and products under real catalytic conditions by conducting transient experiments in a gradientless recycle reactor. A quantitative analysis of the mass transport is managed using a sufficient continuum model. Applying the Maxwell-Stefan approach for multicomponent mass transport in micropores, it was possible to point out the difference between co- and counterdifusion. From our results we conclude that the selectivity is mainly controled by a severe product diffusion limitation due to a strong product-catalyst interaction. Furthermore, the application of a product shape selective Para-Cresol synthesis on HZSM-5 is discussed. Therefore the determined effective diffusion coefficients and the isomerization rate constants enable a detailed simulation study.
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the synthesis of Cresol from toluene and n2o on h al zsm 5 minimizing the product diffusion limitation by the use of small crystals
Catalysis Letters, 2002Co-Authors: B Vogel, C Schneider, Elias KlemmAbstract:The direct hydroxylation of toluene with nitrous oxide to Cresol has been studied on two different H[Al]ZSM-5 zeolites with an Si/Al ratio of around 25 and different crystal sizes (30-70 nm and 1-3 μm). The samples were activated by calcination and characterized by X-ray diffraction, temperature programmed desorption of ammonia, adsorption of nitrogen and transmission electron microscopy. For the two different crystal sizes, different macroscopic Cresol yields and time on stream behaviours are observed. The sample having larger crystals shows a decrease in toluene conversion with increasing reaction temperature. For the smaller crystals an increase in toluene conversion, selectivity to Cresol and amount of Para-Cresol in the Cresol fraction with increasing reaction temperature is observed. The Para-Cresol selectivity is lower on the sample with the longer diffusion path. The findings are explained by product diffusion limitation caused by high reactivity and strong adsorption of the polar product Cresol on H[Al]ZSM-5, resulting in a rapid deactivation of the larger crystals.
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The Synthesis of Cresol from Toluene and N_2O on H[Al]ZSM-5: Minimizing the Product Diffusion Limitation by the Use of Small Crystals
Catalysis Letters, 2002Co-Authors: B Vogel, C Schneider, Elias KlemmAbstract:The direct hydroxylation of toluene with nitrous oxide to Cresol has been studied on two different H[Al]ZSM-5 zeolites with an Si/Al ratio of around 25 and different crystal sizes (30-70 nm and 1-3 μm). The samples were activated by calcination and characterized by X-ray diffraction, temperature programmed desorption of ammonia, adsorption of nitrogen and transmission electron microscopy. For the two different crystal sizes, different macroscopic Cresol yields and time on stream behaviours are observed. The sample having larger crystals shows a decrease in toluene conversion with increasing reaction temperature. For the smaller crystals an increase in toluene conversion, selectivity to Cresol and amount of Para-Cresol in the Cresol fraction with increasing reaction temperature is observed. The Para-Cresol selectivity is lower on the sample with the longer diffusion path. The findings are explained by product diffusion limitation caused by high reactivity and strong adsorption of the polar product Cresol on H[Al]ZSM-5, resulting in a rapid deactivation of the larger crystals.
P. Wiesen - One of the best experts on this subject based on the ideXlab platform.
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Verification of the Contribution of Vehicular Traffic to the Total NMVOC Emissions in Germany and the Importance of the NO_3 Chemistry in the City Air
Journal of Atmospheric Chemistry, 2002Co-Authors: R. Kurtenbach, K H Becker, R. Ackermann, A. Geyer, J. A. G. Gomes, J. C. Lörzer, U. Platt, P. WiesenAbstract:In 1997 and 1998 several field campaigns for monitoring non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NO_x) were carried out in a road traffic tunnel and in the city center of Wuppertal, Germany. C_2–C_10 aliphatic and aromatic hydrocarbons were monitored using a compact GC instrument. DOAS White and long path systems were used to measure aromatic hydrocarbons and oxygenated aromatic compounds. A formaldehyde monitor was used to measure formaldehyde. Chemiluminescence NO analysers with NO_2 converter were used for measuring NO and NO_2. The high mixing ratios of the NMVOCs observed in the road traffic tunnel, especially 2.9 ppbv phenol, 1.5ppbv Para -Cresol and 4.4 ppbv benzaldehyde, in comparison with themeasured background concentration clearly indicate that these compounds were directly emitted from road traffic. Para -Cresol was for the first timeselectively detected as primary pollutant from traffic. From the measured data a NMVOC profile of the tunnel air and the city air, normalised to benzene (ppbC/ppbC), was derived. For most compounds the observed city air NMVOC profile is almost identical with that obtained in the traffic tunnel. Since benzene originates mainly from road traffic emission, the comparison of the normalised emission ratios indicate that the road traffic emissions in Wuppertal have still the largest impact on the city air composition, which is in contrast to the German emission inventory. In both NMVOC profiles, aromatic compounds have remarkably large contributions of more than 40 ppbC%. In addtion, total NMVOC/NO_x ratios from 0.6 up to 3.0ppbC/ppb in the traffic tunnel air and 3.4± 0.5 in the city air of Wuppertal were obtained. From the observed Para -Cresol/toluene and ortho -Cresol/toluene ratios in the city air, evidence was found thatalso during daytime NO_3 radical reactions play an important role in urban air.
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Verification of the Contribution of Vehicular Traffic to the Total NMVOC Emissions in Germany and the Importance of the NO3 Chemistry in the City Air
Tropospheric Chemistry, 2002Co-Authors: R. Kurtenbach, R. Ackermann, A. Geyer, J. A. G. Gomes, J. C. Lörzer, U. Platt, Karl H. Becker, P. WiesenAbstract:In 1997 and 1998 several field campaigns for monitoring non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NO x ) were carried out in a road traffic tunnel and in the city center of Wuppertal, Germany. C2–C10 aliphatic and aromatic hydrocarbons were monitored using a compact GC instrument. DOAS White and long path systems were used to measure aromatic hydrocarbons and oxygenated aromatic compounds. A formaldehyde monitor was used to measure formaldehyde. Chemiluminescence NO analysers with NO2 converter were used for measuring NO and NO2. The high mixing ratios of the NMVOCs observed in the road traffic tunnel, especially 2.9 ppbv phenol, 1.5 ppbv Para-Cresol and 4.4 ppbv benzaldehyde, in comparison with the measured background concentration clearly indicate that these compounds were directly emitted from road traffic. Para-Cresol was for the first time selectively detected as primary pollutant from traffic. From the measured data a NMVOC profile of the tunnel air and the city air, normalised to benzene (ppbC/ppbC), was derived. For most compounds the observed city air NMVOC profile is almost identical with that obtained in the traffic tunnel. Since benzene originates mainly from road traffic emission, the comparison of the normalised emission ratios indicate that the road traffic emissions in Wuppertal have still the largest impact on the city air composition, which is in contrast to the German emission inventory. In both NMVOC profiles, aromatic compounds have remarkably large contributions of more than 40 ppbC%. In addtion, total NMVOC/NO x ratios from 0.6 up to 3.0 ppbC/ppb in the traffic tunnel air and 3.4 ± 0.5 in the city air of Wuppertal were obtained. From the observed Para-Cresol/toluene and ortho-Cresol/toluene ratios in the city air, evidence was found that also during daytime NO3 radical reactions play an important role in urban air.
B Vogel - One of the best experts on this subject based on the ideXlab platform.
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the synthesis of Cresol from toluene and n2o on h al zsm 5 minimizing the product diffusion limitation by the use of small crystals
Catalysis Letters, 2002Co-Authors: B Vogel, C Schneider, Elias KlemmAbstract:The direct hydroxylation of toluene with nitrous oxide to Cresol has been studied on two different H[Al]ZSM-5 zeolites with an Si/Al ratio of around 25 and different crystal sizes (30-70 nm and 1-3 μm). The samples were activated by calcination and characterized by X-ray diffraction, temperature programmed desorption of ammonia, adsorption of nitrogen and transmission electron microscopy. For the two different crystal sizes, different macroscopic Cresol yields and time on stream behaviours are observed. The sample having larger crystals shows a decrease in toluene conversion with increasing reaction temperature. For the smaller crystals an increase in toluene conversion, selectivity to Cresol and amount of Para-Cresol in the Cresol fraction with increasing reaction temperature is observed. The Para-Cresol selectivity is lower on the sample with the longer diffusion path. The findings are explained by product diffusion limitation caused by high reactivity and strong adsorption of the polar product Cresol on H[Al]ZSM-5, resulting in a rapid deactivation of the larger crystals.
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The Synthesis of Cresol from Toluene and N_2O on H[Al]ZSM-5: Minimizing the Product Diffusion Limitation by the Use of Small Crystals
Catalysis Letters, 2002Co-Authors: B Vogel, C Schneider, Elias KlemmAbstract:The direct hydroxylation of toluene with nitrous oxide to Cresol has been studied on two different H[Al]ZSM-5 zeolites with an Si/Al ratio of around 25 and different crystal sizes (30-70 nm and 1-3 μm). The samples were activated by calcination and characterized by X-ray diffraction, temperature programmed desorption of ammonia, adsorption of nitrogen and transmission electron microscopy. For the two different crystal sizes, different macroscopic Cresol yields and time on stream behaviours are observed. The sample having larger crystals shows a decrease in toluene conversion with increasing reaction temperature. For the smaller crystals an increase in toluene conversion, selectivity to Cresol and amount of Para-Cresol in the Cresol fraction with increasing reaction temperature is observed. The Para-Cresol selectivity is lower on the sample with the longer diffusion path. The findings are explained by product diffusion limitation caused by high reactivity and strong adsorption of the polar product Cresol on H[Al]ZSM-5, resulting in a rapid deactivation of the larger crystals.
Zhongmin Liu - One of the best experts on this subject based on the ideXlab platform.
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Highly selective synthesis of Para-Cresol by conversion of anisole on ZSM-5 zeolites
Microporous and Mesoporous Materials, 2014Co-Authors: Wang Kunyuan, Xinglong Dong, Zhaoan Chen, Zhongmin LiuAbstract:A novel route to obtain the high Para-selectivity was developed by conversion of anisole on modified ZSM-5 in a continuous flowing fixed-bed reactor. It showed that the silylation and steaming treatment were significantly benificial to enhance the Para-selectivity. Compared with the parent catalysts, the Para-selectivity was sharply increased from 18.13% to 69.21% after the second silylation, which was further increased to 80.67% by steaming treatment. The acid sites with different strength of catalysts were studied by NH3-TPD which had an influence on both the Para-selectivity and the amount of aromatics in the products.
R. Kurtenbach - One of the best experts on this subject based on the ideXlab platform.
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Verification of the Contribution of Vehicular Traffic to the Total NMVOC Emissions in Germany and the Importance of the NO_3 Chemistry in the City Air
Journal of Atmospheric Chemistry, 2002Co-Authors: R. Kurtenbach, K H Becker, R. Ackermann, A. Geyer, J. A. G. Gomes, J. C. Lörzer, U. Platt, P. WiesenAbstract:In 1997 and 1998 several field campaigns for monitoring non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NO_x) were carried out in a road traffic tunnel and in the city center of Wuppertal, Germany. C_2–C_10 aliphatic and aromatic hydrocarbons were monitored using a compact GC instrument. DOAS White and long path systems were used to measure aromatic hydrocarbons and oxygenated aromatic compounds. A formaldehyde monitor was used to measure formaldehyde. Chemiluminescence NO analysers with NO_2 converter were used for measuring NO and NO_2. The high mixing ratios of the NMVOCs observed in the road traffic tunnel, especially 2.9 ppbv phenol, 1.5ppbv Para -Cresol and 4.4 ppbv benzaldehyde, in comparison with themeasured background concentration clearly indicate that these compounds were directly emitted from road traffic. Para -Cresol was for the first timeselectively detected as primary pollutant from traffic. From the measured data a NMVOC profile of the tunnel air and the city air, normalised to benzene (ppbC/ppbC), was derived. For most compounds the observed city air NMVOC profile is almost identical with that obtained in the traffic tunnel. Since benzene originates mainly from road traffic emission, the comparison of the normalised emission ratios indicate that the road traffic emissions in Wuppertal have still the largest impact on the city air composition, which is in contrast to the German emission inventory. In both NMVOC profiles, aromatic compounds have remarkably large contributions of more than 40 ppbC%. In addtion, total NMVOC/NO_x ratios from 0.6 up to 3.0ppbC/ppb in the traffic tunnel air and 3.4± 0.5 in the city air of Wuppertal were obtained. From the observed Para -Cresol/toluene and ortho -Cresol/toluene ratios in the city air, evidence was found thatalso during daytime NO_3 radical reactions play an important role in urban air.
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Verification of the Contribution of Vehicular Traffic to the Total NMVOC Emissions in Germany and the Importance of the NO3 Chemistry in the City Air
Tropospheric Chemistry, 2002Co-Authors: R. Kurtenbach, R. Ackermann, A. Geyer, J. A. G. Gomes, J. C. Lörzer, U. Platt, Karl H. Becker, P. WiesenAbstract:In 1997 and 1998 several field campaigns for monitoring non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NO x ) were carried out in a road traffic tunnel and in the city center of Wuppertal, Germany. C2–C10 aliphatic and aromatic hydrocarbons were monitored using a compact GC instrument. DOAS White and long path systems were used to measure aromatic hydrocarbons and oxygenated aromatic compounds. A formaldehyde monitor was used to measure formaldehyde. Chemiluminescence NO analysers with NO2 converter were used for measuring NO and NO2. The high mixing ratios of the NMVOCs observed in the road traffic tunnel, especially 2.9 ppbv phenol, 1.5 ppbv Para-Cresol and 4.4 ppbv benzaldehyde, in comparison with the measured background concentration clearly indicate that these compounds were directly emitted from road traffic. Para-Cresol was for the first time selectively detected as primary pollutant from traffic. From the measured data a NMVOC profile of the tunnel air and the city air, normalised to benzene (ppbC/ppbC), was derived. For most compounds the observed city air NMVOC profile is almost identical with that obtained in the traffic tunnel. Since benzene originates mainly from road traffic emission, the comparison of the normalised emission ratios indicate that the road traffic emissions in Wuppertal have still the largest impact on the city air composition, which is in contrast to the German emission inventory. In both NMVOC profiles, aromatic compounds have remarkably large contributions of more than 40 ppbC%. In addtion, total NMVOC/NO x ratios from 0.6 up to 3.0 ppbC/ppb in the traffic tunnel air and 3.4 ± 0.5 in the city air of Wuppertal were obtained. From the observed Para-Cresol/toluene and ortho-Cresol/toluene ratios in the city air, evidence was found that also during daytime NO3 radical reactions play an important role in urban air.
