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Applied Catalysis A, General (v.337, #1)
Stability of rhodium catalysts supported on gadolinium doped ceria under steam reforming conditions by Ulrich Hennings; Rainer Reimert (pp. 1-9).
The stability of rhodium catalysts supported on gadolinium doped ceria for the steam reforming reaction is investigated. Based on the results an activation procedure was developed and stable performance of over 190 h was demonstrated. ▪The stability of rhodium catalysts supported on gadolinium doped ceria for the steam reforming reaction is investigated. High temperature reduction of the fresh catalyst in hydrogen results in the typical symptoms of SMSI. Under steam reforming conditions, and after three subsequent reduction-reaction-oxidation cycles, the catalysts showed stable performance. Based on the results an activation procedure was developed and stable performance of over 190 h was demonstrated.
Keywords: Ceria; Gadolinium; Rhodium; Steam reforming; SMSI; Stability; HR-TEM; Redox behavior
Microemulsion-prepared ruthenium catalyst for syngas production via methane partial oxidation by R. Lanza; P. Canu; S.G. Järås (pp. 10-18).
A Ru catalyst supported on alumina was prepared via microemulsion (ME) and coated onto cordierite monoliths. High methane conversion with very good selectivity towards CO and H2 under every condition tested. The effects of GHSV and heating rate (HR) were investigated, both during heating and cooling. Hysteresis cycles were observed and discussed.▪Partial oxidation of methane (POxM) was studied over Ru catalyst supported on alumina (1%, w/w). The catalyst was prepared via microemulsion (ME) and coated onto cordierite monoliths. Samples were characterized by XRD, BET surface area, SEM–EDS and TPR and TPO analyses. The catalyst showed high methane conversion with very good selectivity towards CO and H2 under every condition tested. The effects of GHSV and heating rate (HR) were investigated, recording composition data both during heating and cooling. This allowed to evidence hysteresis cycles and to obtain additional information on the reactions occurring within the monolith.
Keywords: Microemulsion; Methane; Partial oxidation; Syngas; Ruthenium; Activity; Hysteresis
Effects of preparation methods of ZrO2 support on catalytic performances of Ni/ZrO2 catalysts in methane partial oxidation to syngas by Yue-Qin Song; De-Hua He; Bo-Qing Xu (pp. 19-28).
The physico-chemical properties of Ni/ZrO2 catalysts, in which ZrO2 support was prepared by different methods, were characterized by XRD, TEM, N2-adsorptioin and H2-TPR. The catalytic performances of the catalysts for methane oxidation to syngas were examined at 700°C, 1.0×105ml/(gcath) and ambient pressure, and the effect of preparation methods of ZrO2 support on the catalytic performances was evaluated.▪ZrO2 was prepared by hydrothermal method (denoted as HT method), the method of drying and calcinating of alcogel in N2 (denoted as AN method) and conventional precipitation method (denoted as CP method). And 14%Ni/ZrO2 catalysts were prepared by impregnation method. The physico-chemical properties of supports and catalysts were characterized by XRD, TEM, N2-adsorptioin. The effects of preparation methods of ZrO2 support on the catalytic performances of 14%Ni/ZrO2 in methane partial oxidation (POM) at 700°C, 1.0×105ml/(gcath) and ambient pressure were investigated. The experimental results showed that ZrO2 particles prepared by HT method were uniform and spindle-like with the size of 100nm×400nm, while ZrO2 particles prepared by AN method were spheric and small with the size of 20–40nm. As for ZrO2 prepared by CP method, its particles were un-uniform and the size distribution of its particles was wide from 20 to 100nm. The reaction results of POM illustrated that the 14%Ni/ZrO2 catalysts in which ZrO2 was prepared by HT and AN methods, had small Ni particles and showed high ability of resistance to carbon deposit and high stability of time on-stream (TOS). The 14%Ni/ZrO2-CP catalyst had large Ni particles and showed an serious deactivation within 50h of TOS due to the formation of large amount of carbon deposit on the surface of catalyst. The results from TEM and TPO showed that encapsulated carbon deposit was formed on small Ni particles and was active for oxidation, while carbon nano-tube was mainly formed on large Ni particles and was inert for oxidation.
Keywords: Ni/ZrO; 2; Partial oxidation of methane; Hydrothermal process
Synergistic catalysis effect in SO2 reduction by CO over Sn–Zr-based catalysts by Gi Bo Han; No-Kuk Park; Suk Hoon Yoon; Tae Jin Lee; Ki June Yoon (pp. 29-38).
In this study, the synergistic effect observed in the SO2 reduction by CO over SnO2–ZrO2 catalysts was investigated in detail. From the reactivity tests of the various catalysts, it was established that the applicable mechanism of this study was different from the conventional mechanisms such as the redox and COS intermediate mechanisms. It could be explained by postulating that the synergistic effect of the Sn–Zr-based catalyst was obtained in the SO2 reduction by CO as the following mechanistic pathway: In the first step involving the redox mechanism, SO2 was converted into elemental sulfur and other by-products such as COS because of the lattice oxygen mobility afforded by the redox properties of the SnO2 catalyst. In the second step involving the COS intermediate mechanism, COS produced in the first step was the more effective reducing agent than CO and reacted with SO2 over the ZrO2 catalyst, and then the productivity of elemental sulfur was improved. At that time, the reaction rate of SO2+2COS→3S+2CO2 must have been faster than that of CO+S→COS. The high reactivity of the SnO2–ZrO2 (Sn/Zr=2/1) catalyst at low temperature was thus caused by a synergistic effect resulting of the simultaneous interaction between the redox mechanism and COS intermediate mechanism.The synergistic effect, which was observed in SO2 reduction by CO over SnO2–ZrO2 catalysts, was investigated in detail. As a result, it is suggested that the high reactivity, SO2 conversion of about 100%, of SnO2–ZrO2 (Sn/Zr=2/1) catalyst at 325°C was caused by the synergistic effect resulting from the interaction between the redox mechanism and COS intermediate mechanism.▪
Keywords: SO; 2; reduction by CO; Sn–Zr-based catalyst; Redox mechanism; COS intermediate mechanism; Synergistic effect
Influence of the Co/Al ratio and the temperature of thermal treatment on cobalt speciation and catalytic properties of Co-ZSM-5 prepared by solid-state ion exchange by Mourad Mhamdi; Sihem Khaddar-Zine; Abdelhamid Ghorbel (pp. 39-47).
Physico-chemical and catalytic properties of cobalt-containing ZSM-5 zeolite prepared by solid-state ion exchange were compared as a function of both the Co/Al molar ratio and the temperature of thermal treatment. The catalysts were characterized by chemical analysis, XRD, N2 BET, TEM/EDX, H2 TPR, FTIR, XANES, EXAFS and TPD of NH3. The preparation procedure results in the disappearance of Brønsted acid sites and the creation of new Lewis acid sites, as suggested by TPD of NH3 and FTIR of pyridine adsorption. TEM/EDX shows that for a Co/Al ratio of 1/2, cobalt is present as exchanged ions in the zeolite and as oxide particles on the support; whilst for a Co/Al ratio of 1 or 3/2, a cobalt phyllosilicate phase is present at the outer surface of the zeolite. Catalyst prepared with the Co/Al ratio of 1 at 500°C exhibits high activity and selectivity toward acetonitrile in the ammoxidation of ethane and ethylene.Ammoxidation of ethylene was tested over Co-ZSM-5 catalysts. The Co/Al molar ratio and the temperature of thermal treatment had an important influence on the physico-chemical and catalytic properties. The preparation procedure results in the disappearance of Brønsted acid sites and the creation of new Lewis acid sites. Furthermore, TEM/EDX and EXAFS show that for Co/Al=1 and 3/2, a cobalt phyllosilicate phase is present at the outer surface of the zeolite.▪
Keywords: Solid-state reaction; EXAFS; XANES; Co-ZSM-5; Ammoxidation
Effects of noble metal-doping on Cu/ZnO/Al2O3 catalysts for water–gas shift reaction by Kazufumi Nishida; Ikuo Atake; Dalin Li; Tetsuya Shishido; Yasunori Oumi; Tsuneji Sano; Katsuomi Takehira (pp. 48-57).
Trace amounts of noble metal were doped on Cu/ZnO/Al2O3 catalysts by adopting “memory effect” of hydrotalcite. Ternary Cu/ZnO/Al2O3 (molar ratio Cu/Zn=1/1, Al content 0–25mol%) catalysts were prepared by co-precipitation ( cp) from metal nitrates; a mixture of hydrotalcite (Cu,Zn)6Al2(OH)16CO3·4H2O, and aurichalcite (Cu,Zn)5(CO3)2(OH)6, was formed at pH 9 with NaOH as the pH controller. Finally the sample, cp-Cu/Zn/Al(45/45/10) containing mainly aurichalcite together with a small amount of hydrotalcite, was selected as the precursor for the noble metal-doping. Noble metal-doping was conducted by dipping the precursor calcined at 300°C in aqueous solutions of the noble metal nitrates; hydrotalcite was reconstituted by the “memory effect” and simultaneously noble metals were incorporated. The noble metal-doped samples were calcined at 300°C and tested for the water–gas shift (WGS) reaction. Among the noble metals, Pt was the most effective for stabilizing the catalytic activity although some deactivation due to Cu sintering took place. An intrinsic promoting effect of Pt was clearly observed by evaluating the turnover frequency of the catalyst. Aurichalcite was indispensable for producing active Cu/ZnO sites, whereas a small amount of hydrotalcite was effective for improving the sustainability of the catalyst by the surface modification. It is likely that hydrogen-spillover from trace Pt to active Cu metal not only enhanced the activity via the reduction–oxidation cycle between Cu0 and Cu+ but also stabilized the active Cu metal species against oxidative sintering during the reaction.Trace amount of Pt-doped Cu/ZnO/Al2O3 catalyst prepared by adopting “memory effect” of hydrotalcite showed a sustainable activity for the water–gas shift reaction; hydrogen-spillover from Pt to active Cu metal enhanced the stability of active Cu metal species against oxidative sintering.▪
Keywords: Water–gas shift reaction; Pt-doped Cu/ZnO/Al; 2; O; 3; catalyst; Co-precipitation; Aurichalcite; Hydrotalcite; “Memory effect”
Acidity and defect sites in titanium silicalite catalyst by Gang Yang; Xijie Lan; Jianqin Zhuang; Ding Ma; Lijun Zhou; Xianchun Liu; Xiuwen Han; Xinhe Bao (pp. 58-65).
In situ MAS NMR experiments and density functional calculations were performed to identify a novel defect site in TS-1 zeolite. It was explained why TS-1 zeolite shows Brönsted acidity whereas silicalite-1 not. Moreover, it was found that the Brönsted acidity of TS-1 zeolite is the weakest to best of our knowledge, suggesting potential roles as new acid catalysts. ▪With density functional calculations and in situ29Si and31P MAS NMR experiments, a novel defect site (defect site II, dsII) was identified in titanium silicalite molecular sieve (TS-1 zeolite), supported by the previous experimental results. The conversion from Q3 species [(SiO)3Si(OH)] into Q4-like species [Si(OSi)4] due to TMP adsorption indicated the presence of Brönsted acidity in TS-1 zeolite. The thermodynamic analysis and Ti/Si substitution energies further confirmed that the proton transferring process of defect site II is much facilitated in TS-1 zeolite whereas on the contrary in silicalite-1. With the proton-affinity calculations, the Brönsted acidities of several cation-doped zeolites were found to decrease in the order of Al-ZSM-5>Fe-ZSM-5>B-ZSM-5>TS-1. The Brönsted acidity of TS-1 zeolite is even weaker than that of B-ZSM-5 zeolite, suggesting the potential role as a new acid catalyst. As to silicalite-1, its acidity is even weaker than that of defect site I (dsI) in TS-1 zeolite.
Keywords: Acidity; Defect sites; Density functional calculations; MAS NMR; Proton transfer
Enzyme-catalyzed conversion of phenol by using immobilized horseradish peroxidase (HRP) in a membraneless electrochemical reactor by Seung-Hee Cho; Joonmok Shim; Sung-Hyun Yun; Seung-Hyeon Moon (pp. 66-72).
This study tested the feasibility of a membraneless electrochemical reactor with immobilized horseradish peroxidase (HRP) for the advanced oxidation of phenol. Under the optimal applied potential, the immobilized HRP that was applied on the inorganic porous Celite was stable and hydrogen peroxide (H2O2) was effectively produced. Phenol was degraded into p-benzoquinone, various organic acids and carbon dioxide through the electroenzymatic method. ▪The catalytic conversion of phenol in a membraneless electrochemical reactor with immobilized horseradish peroxidase (HRP) as a biological catalyst was investigated. To introduce HRP into a membraneless electrochemical reactor, we conducted immobilization on the porous Celite beads through aminopropylation with 3-aminopropyltriethoxysilane (3-APTES) and covalent linkage with glutaraldehyde (GA). Under the optimal applied potential determined by the stability of the immobilized HRP in the electric field and the production rate of hydrogen peroxide (H2O2), the aqueous phase of phenol was effectively converted by the electroenzymatic reaction. Phenol was oxidized by the electrochemical and electroenzymatic methods in a membraneless electrochemical reactor with the immobilized HRP, showing that the oxidation of phenol was enhanced by the electroenzymatic method. During the electroenzymatic degradation, phenol was converted into p-benzoquinone, various organic acids and carbon dioxide (CO2).
Keywords: Membraneless electrochemical reactor; Electroenzymatic oxidation; Horseradish peroxidase (HRP); Phenol; Electrogeneration of hydrogen peroxide (H; 2; O; 2; )
Oligomerization of isobutene over dealuminated Y zeolite catalysts by Ji Woong Yoon; Sung Hwa Jhung; Dae Hyun Choo; Seung Jun Lee; Kwan-Young Lee; Jong-San Chang (pp. 73-77).
Relatively stable isobutene conversion and high selectivity for isobutene trimers and tetramers are attained over a dealuminated Y zeolite that was obtained readily by steam-treatment at 600°C. The observed stable operation and increased selectivity for trimers and tetramers are attributed to the high concentration of Lewis acid sites.▪Oligomerization of isobutene to produce oligomers such as trimers and tetramers has been investigated over dealuminated Y zeolite catalysts that were obtained by calcination at temperatures in the range of 500–700°C in the presence of steam. Relatively stable isobutene conversion and high selectivity for trimers and tetramers are attained over a dealuminated Y zeolite by steam-treatment at 600°C. The observed stable performance with the increased selectivity is attributed to the high concentration of Lewis acid sites. Moreover, a deactivated catalyst can be regenerated easily by simple calcination in air. The present study demonstrates that a steamed zeolite having high concentration of Lewis acid sites, even with decreased crystallinity and porosity, is one of the potential catalysts to exhibit stable and high conversion, high selectivity (for trimers and tetramers) and facile regeneration for the oligomerization of isobutene. However, the contribution of a strong or new acid site for the stable catalysis cannot be ruled out.
Keywords: Y zeolite; Dealumination; Isobutene; Oligomerization; Lewis acid site
Deperoxidation of cyclohexyl hydroperoxide by silica-supported alkoxo-tantalum complexes by R. Petroff Saint-Arroman; B. Didillon; A. de Mallmann; J.M. Basset; F. Lefebvre (pp. 78-85).
Silica-supported alkoxo-tantalum complexes were used in the deperoxidation of cyclohexyl hydroperoxide into cyclohexanol and cyclohexanone. The effects of the number of bonds with the silica support and of the nature of the alkoxo ligands were studied. In all cases the activity was quite the same and was relatively good for a heterogeneous catalyst. The main interest of these systems is that there is no leaching of tantalum in the reaction medium, leading to an easy recycling of the catalyst.Silica-supported alkoxo-tantalum complexes are active for the deperoxidation of cyclohexyl hydroperoxide into cyclohexanol and cyclohexanone. The effects of the number of bonds with the silica support and of the nature of the alkoxo ligands were studied. There is no leaching of tantalum in the reaction medium, leading to an easy recycling of the catalyst.▪
Keywords: Tantalum alkoxide; Silica; Deperoxidation; Catalysis; Cyclohexanol; Cyclohexanone
Study of the surface and redox properties of ceria–zirconia oxides by S. Damyanova; B. Pawelec; K. Arishtirova; M.V. Martinez Huerta; J.L.G. Fierro (pp. 86-96).
CeO2–ZrO2 oxides with different CeO2 content (1–12wt%) were prepared by the impregnation method. The effects of CeO2 content, calcination temperature and interaction between the components on the structure and reductive properties of CeO2–ZrO2 oxides were evaluated by using different techniques such as XRD, DRS, FTIR, Raman, XPS, TGA and TPR. Spectroscopic data showed that the tetragonal phase of zirconia is preserved in all CeO2–ZrO2 oxides, although they retain a high number of defect sites caused by a strong interaction between zirconia and cerium oxide species. An enrichment of the zirconia surface with a fluorite structure of CeO2 is observed for the CeO2–ZrO2 oxide with the highest CeO2 content (12wt%). The samples subjected to consecutive reduction–oxidation cycles at different temperatures showed good redox properties related to the increase of oxygen mobility. It was concluded that these CeO2–ZrO2 oxide systems, displaying high surface and good thermal stability, are similar to chemically mixed oxides due to the strong interaction between the zirconia carrier and deposited ceria.The effect of CeO2 content, calcination temperature and interaction between components on the structure and redox properties of CeO2–ZrO2 oxides was evaluated. At the highest CeO2 loading (12wt%) and after high temperature treatment of 1073K an enrichment of the zirconia surface with a fluorite structure of CeO2 is observed in the figure. XRD of CeO2, ZrO2 and CeO2–ZrO2 oxides with different CeO2 content after temperature treatment at 823 (A) and 1073K (B). ▪
Keywords: Ceria–zirconia oxides; XRD; FTIR; DRS; Raman; XPS; TPR
p-Aminophenol synthesis in an organic/aqueous system using Pt supported on mesoporous carbons by Kyung-Il Min; Jung-Sik Choi; Young-Min Chung; Wha-Seung Ahn; Ryong Ryoo; P.K. Lim (pp. 97-104).
The biphasic conversion of nitrobenzene to p-aminophenol (PAP) via Pt/C-catalyzed hydrogenation of nitrobenzene and an acid-catalyzed rearrangement of the N-phenylhydroxylamine intermediate was studied. The effects of Pt/C catalyst loading, type of carbon support, reaction temperature, acid catalyst concentration, and additives were investigated. Pt catalysts supported on novel mesoporous carbons which have uniform pore diameters of 3 and 4.5nm significantly outperform their counterpart supported on activated carbon.▪The biphasic conversion of nitrobenzene to p-aminophenol (PAP) via Pt/C-catalyzed hydrogenation of nitrobenzene and an acid-catalyzed rearrangement of the N-phenylhydroxylamine intermediate was studied. The effects of Pt/C catalyst loading, type of carbon support, reaction temperature, acid catalyst concentration, and additives on the reaction rate and PAP selectivity were investigated. At a given catalyst loading, nitrobenzene conversion and PAP selectivity were favored under a high reaction temperature and a high aqueous acid concentration. An increase in Pt/C catalyst loading leads to an increased hydrogenation rate but a lower PAP selectivity. Nitrobenzene conversion and PAP selectivity are both promoted by a small addition of N, N-dimethyl- n-dodecylamine, which may act as a phase transfer agent or emulsifier. Pt catalysts supported on novel mesoporous carbons – CMK-1 and CMK-3, which have uniform pore diameters of 3 and 4.5nm – significantly outperform their counterpart supported on activated carbon with micropores. Two percent Pt/CMK-1 shows a catalytic activity equivalent to that of 5% Pt/C, but with significantly better PAP selectivity, i.e., 84% compared to 72%.
Keywords: Nitrobenzene hydrogenation; p; -Aminophenol; Biphasic; Mesoporous carbon; Acid-catalyzed rearrangement
Development of a titania nanotube (TNT) loaded site-selectively with Pt nanoparticles and their photocatalytic activities by Kazumoto Nishijima; Takayuki Fukahori; Naoya Murakami; Taka-aki Kamai; Toshiki Tsubota; Teruhisa Ohno (pp. 105-109).
We investigated site-selective deposition of Pt nanoparticles on the inside surface of titania nanotube (TNT) in order to improve the photocatalytic activity of the TNT. TNT loaded site-selectively with Pt nanoparticles by UV irradiation under ethanol vapor showed the highest photocatalytic activity because the transfer rates of electrons were fastest and the active sites on TNT surface were not covered by Pt nanoparticles.▪Site-selective deposition of Pt nanoparticles on a titania nanotube (TNT) was investigated in order to improve the photocatalytic activity of a TNT. TEM images showed that Pt nanoparticles were deposited site-selectively on the inside surface of the TNT by two methods. TNT powder loaded with Pt nanoparticles by UV irradiation under ethanol atmosphere exhibited the highest photocatalytic activity for oxidation of acetaldehyde. When Pt nanoparticles were deposited on only the inside surface of the TNT by UV irradiation, active sites on the TNT were not covered by Pt nanoparticles, resulting in an increase in its photocatalytic activity for oxidation of acetaldehyde.
Keywords: Photocatalysts; Titania nanotube; Site-selective deposition of Pt nanoparticles; Decomposition of acetaldehyde