Dehydrogenation of ethylbenzene in the presence of CO2 using a catalyst synthesized by polymeric precursor method

Catalysts of iron oxide dispersed on Al or Si oxides were prepared via a polymeric precursor derived from the Pechini method and tested in the dehydrogenation of ethylbenzene in the presence of CO₂, in order to contribute with the studies of this reaction. The catalysts were characterized by thermogravimetric analysis (TG), temperature-programmed reduction (TPR), X-ray diffraction (DRX) and temperature-programmed desorption of CO₂ (TPD-CO₂). Analysis of the spent catalysts by TG and Fourier transformed infrared spectroscopy (FT-IR) pointed to the contribution of CO₂ to the coke deposition. The catalytic results suggest that the high initial ethylbenzene conversion is due to the contribution of basic sites, and the CO₂ adsorption in the basic site (lattice oxygen) may compete with the oxidative dehydrogenation of ethylbenzene. Although CO₂ provides the appropriate conditions to lower the consumption of the basic site, it is not able to promote the Fe²⁺ oxidation or to regenerate the basic site (lattice oxygen) in the iron oxide dispersed on Al or Si oxide catalysts.     

Dehydrogenation of Ethylbenzene to Styrene in the Presence of CO2 over Calcined Hydrotalcite-Like Compounds as Catalysts

Calcined hydrotalcite-like compounds were effective catalysts for the dehydrogenation of ethylbenzene in the presence of CO₂ as an oxidant. X-ray diffraction patterns suggested that the catalyst components are distributed uniformly. The activity (areal rate) of Fe(1)/Al(2)/Zn(6) oxide catalyst (molar ratios in parentheses) was the highest among the catalysts tested.     

Co‐Metal Catalysts on SiO2‐TiO2 for Methanol Production from CO2 – Effect of Preparation Methods

The effect of quantity, composition, and different impregnation sequences on the catalytic properties of Cu‐Zn‐Al/SiO₂‐TiO₂ in the CO₂ hydrogenation for methanol production was investigated. The Cu‐Zn‐Al catalysts supported on SiO₂ and TiO₂ were prepared by incipient wetness impregnation. Then, their performances in CO₂ hydrogenation were tested under defined conditions. The composition variation of Cu and Zn catalysts resulted in a high methanol production for Cu catalysts with a higher content of Cu, which was the active site for CO₂ activation. Regarding the metal quantity of catalysts, a relatively low loading of co‐metal (Cu‐Zn‐Al) led to the maximum methanol yield when compared with higher loadings as a result of the largest surface area.     

Dehydrogenation of ethylbenzene and propane over Ga2O3–ZrO2 catalysts in the presence of CO2

Ga₂O₃–ZrO₂ catalysts were prepared by a coprecipitation method. The catalysts were characterized by XRD, Raman, DRS, XPS, SEM, EDX, IR, NH₃-TPD, CO₂-TPD and N₂ adsorption methods. Dehydrogenation of ethylbenzene and propane in the presence of CO₂ over these catalysts has been investigated and compared. Ga₂O₃–ZrO₂ catalysts exhibit different catalytic behavior for the two dehydrogenation reactions.     

Fluorine-modified Cu/Zn/Al/Zr catalysts via hydrotalcite-like precursors for CO2 hydrogenation to methanol

Fluorine-modified Cu/Zn/Al/Zr catalysts were prepared by calcination of the fluorine-containing Cu/Zn/Al/Zr hydrotalcite-like compounds and tested for CO₂ hydrogenation to methanol. The results revealed that the CH₃OH selectivity was greatly improved by the remarkable increase of the proportion of strongly basic sites, while the CO₂ conversion decreased slightly. It is also found that the activity of catalysts is closely related to the synergy between the Cu and basic sites. The CH₃OH yield for the fluorine-modified Cu/Zn/Al/Zr catalysts was higher than that for the fluorine-free catalysts; thus, the introduction of fluorine favored the methanol formation.     

Behaviors of V-doped Titanium Mixed Oxides in the Catalytic Dehydrogenation of Ethylbenzene

By an acid-catalyzed sol–gel method the V-doped titanium oxides (VxDTOs, x _mol% of V/(V + Ti) molar ratio) were prepared and systematically characterized by the techniques of XRD, TEM, H₂-TPR, XPS and TGA, indicating that most of the vanadium in the catalyst was highly dispersed on the surface of and in the bulk phase of TiO₂. The effect of V⁵⁺ doping level (1–9 mol% V⁵⁺) on the surface of TiO₂ and VxDTOs catalytic performance was analyzed. From the catalytic activity evaluation of VxDTOs in the dehydrogenation of ethylbenzene to styrene in the presence of CO₂ (CO₂-EBDH) at 450 °C, V6DTOs catalyst had the highest activity. Its higher activity in CO₂ than in N₂ clearly shows that CO₂ markedly enhanced the dehydrogenation of ethylbenzene. The activity of V6DTOs catalyst could almost be resumed after regeneration by air while partly resumed after regeneration by CO₂.     

In Situ Hydrogenation of CO2 by Al/Fe and Zn/Cu Alloy Catalysts under Mild Conditions

The development of efficient metal catalysts for in situ hydrogenation of CO₂ in water under mild conditions has gained considerable attention. Three Al alloys (Al/Fe, Al/Fe/Cu, Al/Cu) and three Zn/Cu alloys for in situ hydrogenation of CO₂ in aqueous bicarbonate solutions were investigated. Hydrogen was generated by reaction of Al, Fe, and Zn in the alloys with water. In situ hydrogenation of CO₂ was likely to be catalyzed by intermetallic compounds and generated metal oxides. Al alloys catalyzed the hydrogenation to methane while Zn/Cu alloys produced CO and formic acid. Zn/Cu5 possessed the highest catalytic activity, which was attributed to the CuZn5 crystal planes in the alloys. Insights are provided into the importance of compositions and structures of alloys for the selectivity for in situ hydrogenation of CO₂ in aqueous bicarbonate solutions.     

Effect of Structural Promoters on Fe-Based Fischer–Tropsch Synthesis of Biomass Derived Syngas

Biomass gasification and subsequent conversion of this syngas to liquid hydrocarbons using Fischer–Tropsch (F–T) synthesis is a promising source of hydrocarbon fuels. However, biomass-derived syngas is different from syngas obtained from other sources such as steam reforming of methane. Specifically the H₂/CO ratio is less than 1/1 and the CO₂ concentrations are somewhat higher. Here, we report the use of Fe-based F–T catalysts for the conversion of syngas produced by the air-blown, atmospheric pressure gasification of southern pine wood chips. The syngas from the gasification step is compressed and cleaned in a series of sorbents to produce the following feed to the F–T step: 2.78 % CH₄, 11 % CO₂, 15.4 % H₂, 21.3 % CO, and balance N₂. The relatively high level of CO₂ suggests the need to use catalysts that are active for CO₂ hydrogenation as well is resistant to oxidation in presence of high levels of CO₂. The work reported here focuses on the effect of these different structural promoters on iron-based F–T catalysts with the general formulas 100Fe/5Cu/4K/15Si, 100Fe/5Cu/4K/15Al and 100Fe/5Cu/4K/15Zn. Although the effect of Si, Al or Zn on iron-based F–T catalysts has been examined previously for CO+CO₂ hydrogenation, we have found no direct comparison of these three structural promoters, nor any studies of these promoters for a syngas produced from biomass. Results show that catalysts promoted with Zn and Al have a higher extent of reduction and carburization in CO and higher amount of carbides and CO adsorption as compared to Fe/Cu/K/Si. This resulted in higher activity and selectivity to C₅+ hydrocarbons than the catalyst promoted with silica.     

Synthesis of ethylbenzene by alkylation of benzene with diethyl oxalate over HZSM-5

Catalytic synthesis of ethylbenzene by alkylation of benzene with diethyl oxalate was carried out over HZSM-5 with Si/Al ratios from 50 to 250. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ammonia temperature-programmed desorption (NH₃-TPD) and pyridine IR techniques. As revealed by the results of NH₃-TPD and pyridine IR spectra, a significant decrease in acidic strength and the number of acidic sites is observed with increasing Si/Al ratio from 50 to 250. The benzene conversion and ethylbenzene selectivity increases obviously with increasing Si/Al ratio from 50 to 200. With a further increase in Si/Al ratios, a slight decrease in the conversion of benzene and selectivity for ethylbenzene is detected, indicating that a proper acidic strength was required in this reaction. In addition, the effects of temperature and feed ratio on the catalytic activity and product distributions are also investigated in this study.     

A Cu/Zn/Al/Zr Fibrous Catalyst that is an Improved CO<Subscript>2</Subscript> Hydrogenation to Methanol Catalyst

A series of Cu/Zn/Al/Zr CO₂ hydrogenation to methanol catalysts containing different ratios of Al/Zr were prepared using a co-precipitation procedure. SEM, TEM, and XRD characterization showed that all the catalysts comprised crystallites in a fibrous structure and their Cu/Zn crystallite dispersions were better than that of a commercial (COM) catalyst. It is suggested that the high dispersion and stability of the Cu/Zn crystallites due to the fibrous structure enhanced CO₂ hydrogenation, and the added Zr component further improved the catalyst. A 5% Zr addition gave a methanol space time yield 80% higher than that on the COM catalyst.     

Dehydrogenation of ethylbenzene with CO2 over V2O5/Al2O3–ZrO2 catalyst

V-containing catalysts supported on Al₂O₃, modified with varying amounts of ZrO₂, were prepared by impregnation method. Dehydrogenation of ethylbenzene with CO₂ was run over these catalysts in a fixed-bed downflow stainless steel reactor. Compared with pure Al₂O₃ support, a small amount of ZrO₂ in the support led to a significant increase in catalytic activity. Partial reduction of vanadium oxides and carbon deposition were the main reasons for the decreased catalytic activity.     

Oxidative dehydrogenation of n-butane over bimetallic mesoporous and microporous zeolites with CO2 as mild oxidant

Oxidative dehydrogenation of n-butane was tested using carbon dioxide as a mild oxidant over bimetallic Cr–V supported catalysts (MCM-41, ZSM-5, MCM-22 and mesoZSM-5). The textural properties of the catalysts were measured by means of XRD, N₂ adsorption, SEM-EDX, Raman, H₂-TPR, pyridine FT-IR, NH₃ and CO₂-TPD techniques. The metal content of Cr and V was maintained around 1.2 and 2.8 wt% for the catalytic test in packed bed reactor at different temperatures (525–600 °C) for 180 min. 1.2Cr2.8 V/MCM-41 and 1.2Cr2.8 V/ZSM-5 exhibited maximum conversion of 14 and 13.1 %, respectively at 10 min and 600 °C. Significantly, high butenes selectivity was observed over MCM-41 (86.27 %) than ZSM-5 support (58.1 %). The mesoporosity in ZSM-5 had a negative impact on conversion level (7.1 %) but improved the butenes selectivity slightly. 1.2Cr2.8 V/M-22 showed the highest cracking ability leading to overall reduced butenes selectivity (57.9 %). The study shows that over all catalysts, n-butane conversion is independent of CO₂ conversion. 1.2Cr2.8 V/M-22 showed highest CO₂ conversion in the range 2.35–2.2 % between 525 and 550 °C. The apparent activation energies of dehydrogenation and cracking reaction over the four catalysts were evaluated. The ratio of conversion to coke weight per cent over the four catalysts are observed in the following order: 1.2Cr2.8 V/M-41 > 1.2Cr2.8 V/Z-5 > 1.2Cr2.8 V/mesoZ-5 > 1.2Cr2.8 V/M-22.     

Gas-phase conversion of glycerol over mixed metal oxide catalysts

A series of aluminophosphates (APO) catalysts with Ce, Cu, Cr, Fe, Mn, Mo, V, and W oxide loading at a constant ratio M: Al = 1: 10 and PO₄: Al = 1: 12 were prepared and characterized by N₂ physisorption, XRD and NH₃-TPD. Gas-phase dehydration of glycerol to produce acrolein and acetol was investigated at 280°C in presence of water. Conversion and product distribution depended on the intrinsic acidity and the type of transition metal oxide. Best selectivity to acrolein (52–58%) was obtained for W- und Mo-APO catalysts. Cr-, Mn- and W- oxide containing catalysts enhanced the formation of phenol, acetaldehyde and CO _x . The catalysts containing V- and Fe-oxide promoted the formation of allyl alcohol. All catalysts showed long term stability, which can be attributed to the redox ability of the metal oxides that enhances the removal of coke deposits. The investigated catalyst a specially W-APO and Mo-APO can be recommended for further controlled trials on a pilot plant for selective conversion of water solution of glycerol to acrolein and/or acetol.     

The effect of the Ce content on the oxidative dehydrogenation of propane over CrOy-CeO2/γ-Al2O3 catalysts

A series of CrO_y (17.5 wt%)-CeO₂ (X wt%)/γ-Al₂O₃ catalysts (X = 0, 0.5, 2, 5, 8) with various Ce contents were prepared by a wetness impregnation method and were applied to the dehydrogenation of propane to propylene at 550 °C and 0.1 MPa. The prepared catalysts were characterized by BET, H₂-TPR, O₂-TPD, XPS, XRD, SEM-EDS and Raman spectroscopy. Among the prepared catalysts, the 17.5Cr-2Ce/Al catalyst with the largest amount of lattice oxygen exhibited the best catalytic performance for the dehydrogenation of propane to propylene with lattice oxygen. The decreased presence of oxygen defects and reducibility were the factors responsible for the improved dehydrogenation activity of the catalysts. The CeO₂ layer could inhibit the evolution of lattice oxygen (O²⁻) to electrophilic oxygen species (O₂⁻), and the oxygen defects on the catalyst surface were reduced. The inhibited lattice oxygen evolution prevented the deep oxidation of propane or propylene, the average CO_x selectivity decreased from 24.41% (17.5Cr/Al) to 5.71% (17.5Cr-2Ce/Al), and the average propylene selectivity increased from 60.15% (17.5Cr/Al) to 85.05% (17.5Cr-2Ce/Al).     

Comparison of Cu–Ce–Zr and Cu–Zn–Al mixed oxide catalysts for water-gas shift

Cu–Zn–Al and Cu–Ce–Zr mixed oxide catalysts were prepared by two different methods, co-precipitation and flame spray pyrolysis. The performance of the catalysts was evaluated using the water-gas shift reaction with and without CO₂ and H₂ added to the feed. Cu–Ce–Zr catalysts are found not to be superior to Cu–Zn–Al catalysts in terms of initial activity and short-term stability. Their apparent activation energy appears to be less affected by increased concentrations of CO₂ and H₂.     

Synthesis of a magnesium/aluminum/iron layered double hydroxide and its flammability characteristics in halogen‐free,flame‐retardant ethylene/vinyl acetate copolymer composites

Mg–Al–Fe ternary hydrotalcites were synthesized by a coprecipitation method and characterized with powder X‐ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The flame‐retardant effects of Mg/Al–CO₃ layered double hydroxides (LDHs) and Mg/Al/Fe–CO₃ LDHs in an ethylene/vinyl acetate copolymer (EVA) were studied with the limited oxygen index (LOI), the UL‐94 test, and the cone calorimeter test (CCT), and the thermal degradation behavior of the composites was examined by thermogravimetric analysis. The results showed that the LOI values of the EVA/(Mg/Al/Fe–CO₃ LDH) composites were basically higher than those of the EVA/(Mg/Al–CO₃ LDH) composites at the same additive level. In the UL‐94 test, there was no rating for the EVA/(Mg/Al–CO₃ LDH) composite at the 50% additive level, and a dripping phenomenon occurred. However, the EVA/(Mg/Al/Fe–CO₃ LDH) composites at the same loading level of LDHs containing a suitable amount of Fe³⁺ ion reached the V‐0 rating, the dripping phenomenon disappearing. The CCTs indicated that the heat release rate (HRR) of the EVA composites with Mg/Al/Fe–CO₃ LDHs containing a suitable amount of Fe³⁺ decreased greatly in comparison with that of the composites with Mg/Al–CO₃ LDHs. The introduction of a given amount of Fe³⁺ ion into Mg/Al–CO₃ LDHs resulted in an increase in the LOI, a decrease in the HRR, and the achievement of the UL‐94 V‐0 rating. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Oxidative Dehydrogenation of Ethylbenzene with Carbon Dioxide over Metal-Doped Titanium Oxides

Various metal-doped (Fe, V, Zr, Mg) titanium oxides were prepared by an acid-catalyzed sol–gel method and their properties as catalysts were investigated for oxidative dehydrogenation of ethylbenzene in the presence of carbon dioxide. The characterization techniques, XRD, BET, TGA were employed to analyze the features of catalyst. Fe₃Ti catalyst was found to be quite effective among the catalysts tested at 823 K, 39.8% ethylbenzene conversion and 98% styrene selectivity were acquired.     

In situ FT-IR Spectroscopic Studies on the Mechanism of the Catalytic Oxidation of Carbon Monoxide over Supported Cobalt Catalysts

Three types of supported cobalt catalysts (5% as metal Co loading on SiO₂, Al₂O₃ and TiO₂) were prepared by incipient wetness impregnation with aqueous Co(NO₃)₂·6H₂O solution. Then, all catalysts were calcined in air at 400 °C (assigned as 5Co/Si C400, 5Co/Al C400 and 5Co/Ti C400). Their catalytic activities towards the CO oxidation were studied in a continuous flow micro-reactor. Adsorption of carbon monoxide (CO) and the co-adsorption of CO/O₂ over cobalt oxide were further tested under in situ FT-IR. The results showed that both 5Co/Si C400 and 5Co/Al C400 had higher activity than 5Co/Ti C400. The T₅₀ (50% conversion) for both 5Co/Si C400 and 5Co/Al C400 was reached at temperatures as low as ambient temperature. According to the in situ FT-IR analysis, the variation in oxidation of CO was interpreted with different mechanisms, i.e., the reaction between adsorbed CO and lattice oxygen of cobalt oxide, and part of CO₂ formation via carbonates on 5Co/Si C400; both types of carbonates are formed on 5Co/Al C400 to promote the CO oxidation; while both strong adsorption of CO on TiO₂ and CO₂ on cobalt oxide for 5Co/Ti C400 leads to affect the activity.     

Direct synthesis of mesoporous silicalite-1 supported TiO2–ZrO2 for the dehydrogenation of EB to styrene with CO2

Direct synthesis route was developed to support TiO₂–ZrO₂ binary metal oxide onto the carbon templated mesoporous silicalite-1 (CS-1). Metal hydroxide modified carbon particles could play a role as hard template and simultaneously support metal components on the mesopores during the crystallization of zeolites. Such supported TiO₂–ZrO₂ binary metal oxides (TZ/CS-1) showed better resistance to deactivation in the oxidative dehydrogenation of ethylbenzene (ODHEB) in the presence of CO₂. These catalysts were found to be active, selective and catalytically stable (10 h of time-on-stream) at 600 °C for the dehydrogenation of ethylbenzene (EB) to styrene (Sty).     

Total oxidation of volatile organic compounds by vanadium promoted palladium-titania catalysts: Comparison of aromatic and polyaromatic compounds

Vanadium oxide, palladium oxide and mixed Pd/V-supported on titania catalysts have been prepared and tested in the total oxidation of volatile organic compounds (VOCs). A comparative study with two different aromatic VOCs (benzene and naphthalene) has been carried out. For benzene, the mixed Pd/V-catalysts presented the highest catalytic activity. However, whilst studies with benzene led to the formation of CO₂ only, the total conversion of naphthalene to CO₂ was not achieved throughout the full temperature range for naphthalene conversion. A naphthalene conversion to CO₂ of 99% was obtained over Pd/TiO₂, V/TiO₂ and Pd/V/TiO₂ catalysts at 275, 325 and 300 °C, respectively. Therefore, the requirements for an effective benzene total oxidation catalyst cannot be readily extrapolated to larger polycyclic aromatic compounds, as in the naphthalene oxidation the most active catalyst from an environmental point of view is Pd supported on TiO₂.