Dehydrogenation Of Cyclohexanol Research Articles

Study of the deactivation of copper-based catalysts for dehydrogenation of cyclohexanol to cyclohexanone

Catalytic dehydrogenation of cyclohexanol was carried out in the gas phase in a continuous fixed bed reactor under atmospheric pressure. Two commercial catalysts composed by copper chromite and copper zinc oxide were tested. The activity of the catalysts was evaluated at 250°C, with a weight hourly space velocity of 2.89h−1 and at times on stream (TOS) higher than 400h. A slow deactivation of the catalysts was observed during the reaction, obtaining an activity reduction of 50% at TOS=350h, but maintaining 30% conversion at these conditions. Yield higher than 97% to cyclohexanone was obtained with both catalysts, in all the range of TOS studied. The main impurity observed was phenol, obtained from dehydrogenation reaction, and cyclohexene, only obtained with the copper chromite catalysts, and derived from cyclohexanol dehydration. The results of stability and selectivity with these catalysts are better than others reported in the literature. The main causes of the activity loss are associated to the coke deposition over the copper active sites and the increase of the copper metallic crystallite size. The copper zinc oxide also presents a slight blockage of the porous structure due to coke deposition, what can also decrease the catalyst activity.

Dehydrogenation of cyclohexanol on copper containing catalysts: The role of the support and the preparation method

Abstract SiO 2 and Al 2 O 3 supported copper catalysts were prepared by “chemisorption–hydrolysis” or incipient wetness impregnation methods and investigated by XRD, TG-TPR, UV–vis diffuse reflectance and FTIR spectroscopy. Formation of finely dispersed copper oxide species was registered for the samples prepared by “chemisorption–hydrolysis” method, while a significant amount of XRD detectable copper oxide phase is registered for the SiO 2 impregnated one. The latter materials possess higher catalytic selectivity in cyclohexanol dehydrogenation to cyclohexanone.

Influence of the acid/base and redox properties of catalysts in the gas-phase dehydration–dehydrogenation of cyclohexanol on iron and titania containing mesoporous materials

Monocomponent and bicomponent iron and/or titanium modified MCM- 41 materials prepared by direct synthesis at room temperature were investigated using X-ray diffraction (XRD), nitrogen physisorption, UV-Vis diffuse reflectance, FT-IR and Mossbauer spectroscopy. Their catalytic behavior was studied in cylo- hexanol conversion. Materials with high surface area and well-ordered pore struc- ture were obtained. All modified mesoporous silicas possess high activity in cyclohexanol conversion. Bicomponent FeTiMCM-41 catalyst pretreated in hydrogen at 723 K presented the highest activity and selectivity to cyclohexanone.

Phenol Production Kinetic Model in the Cyclohexanol Dehydrogenation Process

A kinetic model of phenol formation in the process of dehydrogenation of cyclohexanol to cyclohexanone has been developed and validated, including variables such as the temperature and the concentr...

Cyclohexanol dehydrogenation over Cu-loaded TiO2 photocatalyst under solar illumination

The liquid-phase selective dehydrogenation of cyclohexanol has been investigated using two classes of catalyst containing either Cu2O or CuO on TiO2 under solar light in deaerated conditions at room temperature using acetonitrile medium in a batch reactor. The effect on dehydrogenation of three conditions, cyclohexanol concentration, copper loading on TiO2, and amount of catalyst, were investigated. The maximum yield of cyclohexanone obtained was 40%. The catalysts were characterized by XRD, UV–DRS, TEM, SEM–EDAX, and XPS. It was found that 1% (w/w) Cu2O/TiO2 was 100% selective for photocatalytic dehydrogenation of cyclohexanol.

Production of hydrogen through the coupling of dehydrogenation and hydrogenation for the synthesis of cyclohexanone and furfuryl alcohol over different promoters supported on Cu–MgO catalysts

Cu–MgO is found to be an efficient catalyst for the coupling reaction of furfural (FAL) hydrogenation and cyclohexanol (CyOH) dehydrogenation. This process is not only efficient in compensating the thermodynamic equilibrium constraints in the cyclohexanol dehydrogenation and improving the yields towards cyclohexanone but also is a economical route for the synthesis of furfuryl alcohol (FFA) and cyclohexanone (Cyone) as the process do not need any external pumping of hydrogen. The effect of incorporation of various promoters viz., Co, Zn, Fe, Cr, Pd and Ni in Cu–MgO over its activity towards this coupling reaction has been studied. Incorporation of Cr in Cu–MgO catalyst is found be an advantageous in enhancing the yields of both FFA and Cyone. All other promoters though found to show higher activity for the individual reactions of FAL hydrogenation and CyOH dehydrogenation, failed to do the same in their coupling reaction. The stabilization of active species (Cu +/Cu 0) by Cr which also seem to increase the synergetic interaction between Cu and MgO as observed from higher dispersion of copper (from XRD results) and easier reducibility of copper oxide (from TPR results) seem to be the factors behind its higher activity over other promoted catalysts.

Comparative dehydrogenation of cyclohexanol to cyclohexanone with commercial copper catalysts: Catalytic activity and impurities formed

Catalytic dehydrogenation of cyclohexanol to cyclohexanone has been carried out on phase gas in a continuous fixed bed reactor under atmospheric pressure. Copper chromite and copper zinc oxide catalysts have been checked. Effect of temperature (in the range 250–290°C) and spatial time in reactor have been studied. The catalytic activity has been evaluated in terms of cyclohexanone yields and impurities from secondary reactions of dehydration and dehydrogenation of cyclohexanol have also been identified and quantified by GC/MS.Catalysts have been characterized by X-ray diffraction, temperature programmed desorption of ammonia and BET surface area measurement. High activity was confirmed by copper-based catalysts under the operating conditions, concerning the size and dispersion of the copper specie. It was also found that catalysts with alumina and chromium exhibit higher dehydration capacity, being cyclohexene the main impurity obtained. For a given cyclohexanone yield the impurities from dehydrogenation reactions showed similar trends for the three catalysts tested. Phenol was the main impurity obtained by dehydrogenation.

ChemInform Abstract: Dehydrogenation of Cyclohexanol to Cyclohexanone Catalyzed by Tin Oxide and the Sulfated Tin Oxide.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Dependence of Selectivity on the Preparation Method of Copper/α- Alumina Catalysts in the Dehydrogenation of Cyclohexanol.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Effects of the preparation method and calcination temperature on Cu–Cr–Mg–Al catalysts for the dehydrogenation of cyclohexanol

The activities of the Cu–Cr–Mg–Al catalysts in the dehydrogenation of cyclohexanol to cyclohexanone were correlated with particle sizes and the reducibility of the copper species based on XRD and TPR characterizations. Cu0 was proven to be the active center of the catalysts calcined at low temperatures and some solid solution (MgCu2O3) and spinel (CuAl2O4 or MgAl2O4) were produced when the calcination temperature reached 1,000 °C. The Cu–Cr–Mg–Al catalyst prepared by the co-precipitation method and calcined at 400 °C showed the best activity, with a conversion of 79.7% and a selectivity of 98.6% at 300 °C.

Effect of carriers and additives on the activity and stability of copper-based catalysts for the dehydrogenation of cyclohexanol

A continuous process for the dehydrogenation of cyclohexanol to cyclohexanone on copper-based catalysts was described. The catalysts were characterized by XRD, XPS and TPR, and Cu0 was found to be the active site for the copper-based catalysts studied. The two carrier catalysts were proved to be more active than the single carrier ones, and the Cr additive, which mainly existed as the CuCr2O4 phase on the catalyst’s surface, was found to have a significant effect on the activity and stability of the Cu-Cr-Mg-Al catalyst.

Süd-Chemie 2007: Business performance of Catalysts division

A deactivation study of a commercial copper zinc oxide catalyst (T-2130, Süd-Chemie) used in dehydrogenation of cyclohexanol to cyclohexanone in the gas phase has been carried out. The experiments were performed in a continuous fixed bed reactor (tubular stainless steel, inner diameter 0.85 cm, length 25 cm), at 290 °C and atmospheric pressure, at different times on stream (0–200 h) and space times (W/FOLo ratios from 10.5 to 37.4 gcat h/mol). Pseudo steady state cyclohexanol conversions in the range of 16–48% were reached. A constant residual coke of about 7 wt.% of the total weight of catalyst was found at higher space time. The effect of gas composition (cyclohexanol, cyclohexanone and hydrogen) in the feed on both cyclohexanol conversion decay and coke formation was studied. The coke content increased as the cyclohexanone content in the reaction media did, meanwhile coke content was lower when hydrogen concentration was increased. A residual activity of about 30% respect to initial activity was achieved at high times on stream. This value depends on the gas mixture, being lower when cyclohexanone concentration increases or hydrogen concentration decreases.Several deactivation rate equations were tested as a function of the feed composition and the residual activity. The corresponding kinetic parameters were estimated. The cyclohexanol conversion was predicted by coupling the reaction rate of the fresh catalyst with the deactivation rate here obtained. The results confirm the great influence of cyclohexanone on both catalyst deactivation and residual activity. In contrast, hydrogen prevents the coke formation.Solid-state 13C CP-MAS NMR spectroscopy, thermogravimetrical analysis and X-ray photoelectron spectroscopy were performed to analyze the nature of coke deposited on catalyst surface. The results indicate that the nature of coke depends on the feed composition and time on stream.

Correlation between reduction potential of vanadium-containing heteropolyacid (HPA) catalysts and their oxidation activity for cyclohexanol dehydrogenation

Vanadium-containing H6+xP2Mo18−xVxO62 (x = 0, 1, 2 and 3) Wells-Dawson heteropolyacid (HPA) and H3+xPMo12−xVxO40 (x = 0, 1, 2 and 3) Keggin HPA catalysts were applied to the vapor-phase dehydrogenation of cyclohexanol. The catalytic oxidation activity showed a volcano-shaped curve with respect to vanadium substitution for both families of HPA catalysts. The Wells-Dawson HPA showed a better catalytic oxidation performance than the Keggin HPA at the same level of vanadium substitution.

A highly active Cu-MgO-Cr 2O 3 catalyst for simultaneous synthesis of furfuryl alcohol and cyclohexanone by a novel coupling route—Combination of furfural hydrogenation and cyclohexanol dehydrogenation

A novel coupling route highlighting the combination of hydrogenation of furfural and dehydrogenation of cyclohexanol in vapor phase conditions over Cu-MgO-Cr 2O 3 catalyst is highly advantageous in terms of avoiding external pumping of H 2 and maintaining the formation of furfuryl alcohol and cyclohexanone, the desired products, respectively, in good amounts at atmospheric pressure. The catalytic activity of this catalyst is compared with a Cu-MgO coprecipitated catalyst and a copper chromite (commercial Cu-1800P supplied by M/s. Engelhard Corp., USA) catalyst. Cu-MgO-Cr 2O 3 catalyst is prepared by coprecipitation method using tetraethyl ammonium hydroxide as precipitating agent. All the catalysts are characterized by BET surface area, temperature programmed reduction, XRD and XPS. The BET surface area of Cu-MgO-Cr 2O 3 catalyst is higher indicating the presence of smaller Cu particles. XRD results also indicate the presence of smaller particles of Cu in Cu-MgO-Cr 2O 3 catalyst. XPS results indicate the presence of Cu species (Cu 0/Cu +) at the surface of Cu-MgO-Cr 2O 3 catalyst. The higher yields of the products over the Cu-MgO-Cr 2O 3 catalyst in independent and combined reactions compared to the other two catalysts may be attributed to the promotional effect of Cr 2O 3, smaller Cu particle size and more number of Cu 0/Cu + species at the surface.

Study on Cu–Mn–Si catalysts for synthesis of cyclohexanone and 2-methylfuran through the coupling process

Abstract A series of Cu–Mn–Si catalysts for synthesis of cyclohexanone (CHN) and 2-methylfuran (2-MF) through the coupling of cyclohexanol (CHL) dehydrogenation and furfural (FFA) hydrogenation were prepared by co-precipitation method. The catalysts were characterized by using N 2 physisorption, X-ray diffraction (XRD), H 2 temperature programmed reduction (H 2 -TPR), N 2 O-chemisorption and ammonia temperature-programmed desorption (NH 3 -TPD) methods. The results show that metal–silica/or metal–metal interactions are presented in the catalysts, and the contents of copper, manganese and silicon affect the BET surface area, acidity and copper dispersion. The results of the catalytic tests indicate that manganese increases the activity of CHL dehydrogenation and FFA hydrogenation as well as the selectivity of 2-MF. A Cu–Mn–Si catalyst including appropriate copper, manganese and silicon is found to be most active, selective and stable under reaction conditions.

Characterization and reductive amination of cyclohexanol and cyclohexanone over Cu/ZrO2 catalysts

Reductive amination of cyclohexanol/cyclohexanone was studied over copper catalysts supported on zirconia. The effect of copper loading and dispersion was studied on the activity and selectivity of the reaction. A series of zirconia supported copper catalysts with varying copper loadings (1–15 wt%) were prepared by incipient wet impregnation method. The catalysts were characterized by X-ray diffraction (XRD) and temperature-programmed reduction (TPR). Copper dispersion and metal area were determined by N2O decomposition by passivation method. X-ray diffraction patterns indicate the presence of crystalline CuO phase from 4.0 wt% Cu on zirconia. TPR patterns reveal the presence of highly dispersed copper oxide at lower temperatures and bulk CuO at higher temperatures. The acid–base properties of catalysts were investigated by means of a model reaction cyclohexanol dehydrogenation to cyclohexanone and compare with the results of TPD of ammonia, which allows to measure the acid–base properties of the support and to investigate the changes in surface acidity or basicity, resulting from the metal impregnation.

A New Process for Synthesis of γ‐Butyrolactone and Cyclohexanone

AbstractA new process through the coupling of maleic anhydride hydrogenation and cyclohexanol dehydrogenation has been studied for the simultaneous synthesis of γ‐butyrolactone and cyclohexanone. The possibility of the coupling process has been investigated thermodynamically. The separated hydrogenation of maleic anhydride, the dehydrogenation of cyclohexanol, and the coupling process over the same Cu‐Zn‐Al catalyst have been carried out in a fixed‐bed reactor. Compared to conventional processes, the coupling process has several advantages, e.g., improved γ‐butyrolactone and cyclohexanone yields, good energy efficiency, and optimal hydrogen utilization. The effects of reaction temperature, n(H2)/n (reactants) and liquid hourly space velocity on the coupling process are investigated. One thousand hours of stability testing shows that the Cu‐based catalyst has relatively high activity and good stability in the coupling process.

Dehydrogenation of cyclohexanol on Cu–ZnO/SiO2 catalysts: The role of copper species

For the dehydrogenation of cyclohexanol a series of Cu–ZnO/SiO2 catalysts with various Cu to ZnO molar ratios was prepared using the impregnation method, with the loading of copper fixed at 9.5 at.%. The catalysts were characterized by XPS, H2–N2O titration, BET, H2-TPR, NH3-TPD and XRD techniques. The results indicate that the addition of ZnO can improve the dispersion of copper species on reduced Cu–ZnO/SiO2 (CZS) catalysts. Cu0 and Cu+ species were found on the reduced CZS catalysts surface, and the amount of Cu+ increased with the content of ZnO increasing. The addition of ZnO increased the acidity of the CZS catalysts. However, only Cu0 species can be found on the reduced Cu/SiO2 (CS) catalyst surface. According to the reaction results, we found that the selectivity to phenol was related to the amount of Cu+ species, the Cu+ species should be the active sites for the production of phenol, the Cu0 is responsible for cyclohexanol dehydrogenation to cyclohexanone.

Transfer Dehydrogenation of Alcohols over Ceria-Supported Cu, Ir, and Pd Catalysts

Abstract Ceria-supported Cu, Ir, and Pd catalysts showed quite promising activity for transfer dehydrogenation of cyclohexanol and 2-octanol to cyclohexanone and 2-octanone, respectively, using styrene as the hydrogen acceptor. The Cu/CeO2 and Pd/CeO2 catalysts were more active than the previously reported Cu and Pd catalysts supported on Al2O3, and the Ir/CeO2 catalyst exhibited extremely high activity. The reactivity of alcohols decreased in the order 2-octanol > cyclohexanol > benzyl alcohol > 1-octanol. The synergistic effect between the metals and CeO2 as well as the effective coupling of dehydrogenation of alcohols and hydrogenation of styrene was responsible for the high catalytic activity.

Preparation of MgO-Supported Cu2O Catalyst and Its Catalytic Properties for Cyclohexanol Dehydrogenation

Abstract To obtain a more effective catalyst for the dehydrogenation of cyclohexanol to cyclohexanone, the MgO-supported Cu 2 O catalyst was prepared by chemical reduction combined with impregnation using MgO as the support and hydrazine hydrate as the reducing agent. The effects of the preparation conditions on the catalytic properties of the catalyst were studied, and the catalyst was characterized by N 2 adsorption, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy, and temperature-programmed reduction. Cu 2 O is reduced to Cu 0 when the amount of N 2 H 4 ·H 2 O used is high. With increasing amount of NaOH used, catalyst particles congregate and the specific surface area of catalyst decreases. The catalyst activity for dehydrogenation of cyclohexanol reaches the maximum at a molar ratio Cu 2+ :N 2 H 4 ·H 2 O:NaOH of 1:1:2. The catalyst reduced by N 2 H 4 ·H 2 O is composed of only Cu + , whereas the traditional Cu/MgO catalyst contains Cu 0 and a little Cu + . Because Cu + is more active than Cu 0 , the activity of the Cu 2 O/MgO catalyst is much higher than that of the traditional Cu/MgO catalyst.