Size-controlled Pd nanoparticles supported on α-Al2O3 as heterogeneous catalyst for selective hydrogenation of acetylene

Size-controlled Pd nanoparticles （PdNPs） were synthesized in aqueous solution, using sodium car-boxymethyl cellulose as the stabilizer. Size-controlled PdNPs were supported onα-Al2O3 by the incipient wetness impregnation method. The PdNPs onα-Al2O3 support were in a narrow particle size distribution in the range of 1-6 nm. A series of PdNPs/α-Al2O3 catalysts were used for the selective hydrogenation of acetylene in ethylene-rich stream. The results show that PdNPs/α-Al2O3 catalyst with 0.03%（by mass） Pd loading is a very effective and sta-ble catalyst. With promoter Ag added, ethylene selectivity is increased from 41.0%to 63.8%at 100 ＆#176;C. Comparing with conventional Pd-Ag/α-Al2O3 catalyst, PdNPs-Ag/α-Al2O3 catalyst has better catalytic performance in acety-lene hydrogenation and shows good prospects for industrial application.     

Highly selective hydrogenation of phenol and derivatives over Pd catalysts supported on SiO2 and γ-Al2O3 in aqueous media

Pd/Al₂O₃ and Pd/SiO₂ catalysts containing Pd nanoparticles in the size range of 3–13 nm were prepared and investigated in direct selective hydrogenation of phenol to cyclohexanone. Catalysts with 3 nm Pd nanoparticles present highly active and promoted the selective formation of cyclohexanone under atmospheric pressure of hydrogen in aqueous media without additives. Conversion of 99% and a selectivity higher than 99% were achieved within 3 h at 333 K. The generality of Pd/Al₂O₃ catalyst with 3 nm Pd nanoparticles for this reaction was demonstrated by selective hydrogenation of other hydroxylated aromatic compounds with similar performance.     

Plasma-driven CO2 hydrogenation to CH3OH over Fe2O3/γ-Al2O3 catalyst

We report a plasma-assisted CO₂ hydrogenation to CH₃OH over Fe₂O₃/γ-Al₂O₃ catalysts, achieving 12% CO₂ conversion and 58% CH₃OH selectivity at a temperature of nearly 80°C atm pressure. We investigated the effect of various supports and loadings of the Fe-based catalysts, as well as optimized reaction conditions. We characterized catalysts by X-ray powder diffraction (XRD), hydrogen temperature programmed reduction (H₂-TPR), CO₂ and CO temperature programmed desorption (CO₂/CO-TPD), high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), x-ray photoelectron spectroscopy (XPS), Mössbauer, and Fourier transform infrared ( FTIR). The XPS results show that the enhanced CO₂ conversion and CH₃OH selectivity are attributed to the chemisorbed oxygen species on Fe₂O₃/γ-Al₂O₃. Furthermore, the diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) and TPD results illustrate that the catalysts with stronger CO₂ adsorption capacity exhibit a higher reaction performance. In situ DRIFTS gain insight into the specific reaction pathways in the CO₂/H₂ plasma. This study reveals the role of chemisorbed oxygen species as a key intermediate, and inspires to design highly efficient catalysts and expand the catalytic systems for CO₂ hydrogenation to CH₃OH.     

CH4 reforming with CO2 for syngas production over nickel catalysts supported on mesoporous nanostructured γ-Al2O3

Nanostructured γ-Al₂O₃ with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, BET, TPR, TPH, SEM and TPO techniques. The BET analysis showed a high surface area of 204m²g^?1 and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The results revealed that an increase in nickel loading from 5 to 15 wt% decreased the surface area of catalyst from 182 to 160 m²g^?1. In addition, the catalytic results showed an increase in methane conversion with increase in nickel content. TPO analysis revealed that the coke deposition increased with increasing in nickel loading, and the catalyst with 15 wt% of nickel showed the highest degree of carbon formation. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Increasing CO₂/CH₄ ratio increased the methane conversion. The BET analysis of spent catalysts indicated that the mesoporous structure of catalysts still remained after reaction.     

Catalytic conversion of CCl2F2 on a γ-Al2O3 catalyst

Reaction of hydrogen with CCl₂F₂ has been studied on a -Al₂O₃ catalyst at 300°C. Pure -Al₂O₃ appears to be unselective in the catalytic conversion of CCl₂F₂, however, halogenated alumina showed high activity in a reaction leading to the formation of disproportionation products.     

Alkaline earth metal oxides on γ-Al2O3 supported Co catalyst and their application to mercaptan oxidation

γ-Al₂O₃-supported alkaline earth metal oxide samples with different MgO, CaO, SrO and BaO loadings have been prepared by impregnating γ-Al₂O₃ with alkaline earth metal nitrate solutions and then calcining at 773 K and 1,023 K. The resultant samples have been characterized by XRD, EDS coupled with SEM, CO₂-TPD and BET. After preparation of the γ-Al₂O₃-supported alkaline earth metal oxide samples and impregnation with the liquid catalyst LCPs30, supplied by Axens, the catalytic performance of these catalysts was evaluated in the mercaptan oxidation reaction. Results showed that magnesium base oxide is formed at 773 K and base oxides of calcium, barium and strontium are formed at 1,023 K. Catalysts with higher mole ratios have higher conversions and the basicity increases with increasing base oxide loading in the samples. Furthermore, the conversion of mercaptans increases with increasing atomic number of the alkaline earth metal, excluding MgO, which has the highest conversion compared to the other base oxides.     

Complete oxidation of formaldehyde at ambient temperature over γ-Al2O3 supported Au catalyst

Au supported on γ-Al₂O₃ prepared by deposition–precipitation (DP) using urea is found to be a highly active catalyst for the total oxidation of HCHO at room temperature under humid air, without the need for a reducible oxide as support. In-situ DRIFTS studies suggested that the surface hydroxyl groups played a key role in the partial oxidation of HCHO into the formate intermediates, which can be further oxidized into CO₂ and H₂O with participation of nano-Au. This study challenges the traditional idea of supporting noble metals on reducible oxides for HCHO oxidation at room temperature.     

Preparation of highly active nickel catalysts supported on mesoporous nanocrystalline γ-Al2O3 for CO2 methanation

In this study, a group of Ni catalysts supported on mesoporous nanocrystalline γ-Al₂O₃ with high surface area and with different Ni contents was prepared and employed in carbon dioxide methanation reaction. The obtained results showed increasing in nickel content from 10 to 25 wt.% decreased the specific surface area of catalysts from 177 to 130 m²/g and increased the nickel crystallite size from 12 to 24 nm. In addition, increasing in nickel content increased the reducibility of catalyst. The catalytic results revealed that the catalyst with 20 wt.% of Ni possessed high activity and stability in CO₂ methanation reaction.     

Synthesis,structure and characterization of (NH4)2[Cu2(H2O)4(NH3CH2COO)2(NH2CH2COO)2]H2V10O28·6H2O

The decavanadate with a novel glycine–glycinato complex of copper (II) in the cationic part, (NH₄)₂[Cu₂(H₂O)₄(NH₃CH₂COO)₂(NH₂CH₂COO)₂]H₂V₁₀O₂₈·6H₂O (1), has been prepared and characterized by elemental analysis, infrared and EPR spectroscopies. The triplet X band EPR spectrum of powdered sample evidenced magnetic interaction between the Cu(II) atoms in the dimeric unit which is probably realized through the bridging water molecules in this part of the complex. A single crystal X-ray diffraction study revealed that the structure of 1 contains cationic copper complex with a rare Cu(H₂O)₂Cu double bridge. In this cation, a simultaneous bidentate N, O– and monodentate O– coordination of glycine to the same central atom was observed for the first time.     

Direct catalytic synthesis of ε-caprolactam from cyclohexanol using [n-C16H33N (CH3)3]H2PW12O40 as a catalyst

ε-Caprolactam was synthesized directly from cyclohexanol via a tandem catalytic process using [n-C₁₆H₃₃N(CH₃)₃]H₂PW₁₂O₄₀ as a catalyst. The highly efficient performance of the catalysts is due to the phase-transfer function of cation, improved coordination with peroxotungsten during oxidation and stabilization function of heteropoly anion on the intermediate formed during Beckmann rearrangement. A ε-caprolactam yield of 73.9% was obtained with a cyclohexanol conversion of 97.1% under optimized conditions.     

Crystalline mesoporous γ-Al2O3 supported palladium: Novel and efficient catalyst for Suzuki–Miyaura reaction under controlled microwave heating

Crystalline mesoporous γ-Al₂O₃ has been successfully synthesized under high temperature hydrothermal conditions and used as an excellent support for Pd(OAc)₂. The resulting γ-Al₂O₃–Pd showed excellent catalytic activity for Suzuki–Miyaura cross-coupling reaction. As low as 0.2 mol% loading of Pd was needed to obtain cross-coupling products in good to excellent yields in aqueous DMF under microwave irradiation. Moreover, the novel catalyst can be easily recovered by filtration and reused without any diminishing observable activity after five runs.     

CO hydrogenation on Co/γ-Al2O3 and CoRe/γ-Al2O3 studied by SSITKA

Co/γ-Al₂O₃ and CoRe/γ-Al₂O₃ catalysts have been studied by the steady-state isotopic transient kinetic analysis (SSITKA) technique. It was found that neither the CO partial pressure, the temperature nor the space velocity influences the in situ CO adsorption. The space velocity, H₂/CO ratio and temperature was found to affect the intrinsic activity ( ) slightly, while the total pressure and syngas partial pressure had only a negligible effect. The surface concentrations and coverages were, however, unaffected by the space velocity, temperature, total pressure, syngas partial pressure and H₂/CO ratio. All changes, however, affected the methane selectivity, indicating that the methane selectivity was not a function of the surface inventory of methane precursors.     

Ligandless palladium supported on SiO2–TiO2 as effective catalyst for Suzuki reaction

TiO₂–SiO₂ mixed oxides were prepared by the homogeneous precipitation method, and the supports were characterized by XRD, IR and BET. Ligandless palladium supported on SiO₂–TiO₂ was prepared by the deposition–precipitation method and used as recoverable catalyst for Suzuki reactions. The results revealed that the supported catalyst Pd/SiO₂–TiO₂ exhibited excellent catalytic activity for the coupling of aryl bromides with arylboronic acid, and also exhibited moderate catalytic activity for the coupling of aryl chlorides. The catalyst was recycled by simple filtration and reused without further disposal, no significant Pd leaching and loss of catalytic activity was observed except the first reuse.     

Transient study of the dry reforming of methane over Pt supported on different γ-Al2O3

CO₂ reforming of methane has been studied over Pt/Al₂O₃ model catalysts in a temperature range of 600–800 °C using steady-state and transient methods (Transient Response Method (TRM) and DRIFT-MS). Pt-supported catalysts were prepared using two different alumina (γ-Al₂O₃(S) Sasol-Puralox and a synthesized γ-Al₂O₃(N) with nanofibrous structure). Catalysts and supports were characterized by conventional methods (XRD, TEM, A_BET, XPS) before and after reaction. Pt⁰ species are present in the catalysts, with a higher relative contribution for the catalyst that has a nanostructured support. Pt/γ-Al₂O₃(N) catalyst presented the best performance in reactivity and showed a low rate of carbon formation and a minimal water production. From TRM and DRIFT-MS results it can be concluded that, when CO₂ and CH₄ are fed separately into the reaction system, they are activated over the catalytic surface. Besides, when both reactants are fed contemporaneously the presence of CH_X species promotes the CO₂ activation that is responsible for the reforming reaction.     

NiMoNx/γ-Al2O3 catalyst for HDN of pyridine

A series of NiMoN_x/γ-Al₂O₃ catalysts with various Ni contents were prepared by a topotactic reaction between their corresponding precursors NiO·MoO₃/γ-Al₂O₃ and NH₃. The catalysts were characterized using BET, XRD, and H₂-TPR techniques, and the HDN activity of pyridine over these catalysts was tested. XRD patterns show that metallic Ni, Mo₂N and a new phase of Ni₃Mo₃N exist in NiMoN_x/γ-Al₂O₃ catalyst. H₂-TPR studies indicate that the presence of Ni lowers the reduction temperature of the passivated surface layer of nitrided Mo/γ-Al₂O₃. The HDN activity for NiMoN_x/γ-Al₂O₃ is much higher than that for NiMoS_x/γ-Al₂O₃. The nitride catalyst with about 5.0 wt% NiO and 15.0 wt% MoO₃ in its precursor has the highest specific denitrogenation activity. The appearance of Ni₃Mo₃N and the synergy between metallic Ni and nitrided Mo are probably responsible for the high activity of NiMoN_x/γ-Al₂O₃ catalyst. The role of Ni in HDN reaction was also investigated. The activities decrease in the order: reduced Ni/γ-Al₂O₃≥nitrided Ni/γ-Al₂O₃>partially reduced Ni/γ-Al₂O₃ and sulfided Ni/γ-Al₂O₃.     

Ru-Pt catalysts supported on Al2O3 and SiO2─Al2O3 for the selective ring opening of naphthenes

Alumina and silica-alumina supported Ru-Pt catalysts were evaluated for the ring opening of naphthenes. Pt, Ru, and Ru-Pt catalysts were prepared by the impregnation of inorganic precursors over γ-alumina and silica-alumina supports. The catalysts were evaluated by temperature programmed reduction (TPR), pyridine temperature programmed desorption (TPD), CO-FTIR, and by test reactions of 33DM1B isomerization, cyclohexane dehydrogenation, cyclopentane hydrogenolysis, and the ring opening of decalin. The strong interaction between the metals (Pt-Ru) was attributed to their reductions occurring simultaneously. The acidity and strength of the acid sites of the monometallic Ru catalyst were higher than those of the monometallic Pt catalyst. The total acidity (Lewis and Brønsted) and the strength of the acid sites were higher for the silica-alumina supported catalysts. The silica-alumina catalysts had 10 times more Brønsted acidity than the γ-alumina ones and an increased activity and selectivity to decalin ring opening products. Supported monometallic Ru had the best performance for the ring opening reaction.     

Beneficial effect of adding γ-AlOOH to the γ-Al2O3 washcoat of a PdO catalyst for methane oxidation

The beneficial effect of adding γ-AlOOH to the γ-Al₂O₃ washcoat of a ceramic cordierite (2MgO · 2Al₂O₃ · 5SiO₂) monolith, used to support a PdO catalyst, is reported for methane oxidation in the presence of water at low temperature (<500°C). The mini-monolith (400 cells per square inch (CPI), 1 cm diameter × 2.54 cm length; ~52 cells) was washcoated using a suspension of γ-Al₂O₃ plus boehmite (γ-AlOOH), followed by calcination and then deposition of Pd by wet impregnation. An optimum solid content of 25 wt% in the washcoat suspension was used to obtain a ~25 wt% washcoat on the monolith. The presence of γ-AlOOH enhanced the thermal and mechanical stability of the washcoat, provided that the γ-AlOOH content was <8 wt%. Temperature-programmed methane oxidation (TPO) showed that the addition of γ-AlOOH to the γ-Al₂O₃ washcoat decreased the catalyst activity. However, when H₂O (2 vol% and 5 vol%) was present in the feed gas, the γ-AlOOH improved the catalyst activity and stability. A γ-AlOOH content of ~5 wt% in the washcoat was determined to provide the highest catalyst activity and stability for CH₄ oxidation in the presence of water.     

Preparation of Pd/γ-Al2O3/nickel foam monolithic catalyst and its performance for selective hydrogenation in a rotating packed bed reactor

Selective hydrogenation plays an important role in chemical industries,yet its selectivity is usually lim-ited by the mass transfer.In this work,the enhanced hydrogenation selectivity was achieved in a rotating packed bed (RPB) reactor with excellent mass transfer efficiency.Aiming to be used under the centrifugal filed,a monolithic catalyst Pd/γ-Al2O3/nickel foam suiting for the shape and size of the rotor of RPB reac-tor was prepared by the electrophoretic deposition method.The mechanical strength of the catalyst can meet the requirement of high centrifugal force in the RPB.The hydrogenation selectivity in the RPB reac-tor using the 3-methyl-1-pentyn-3-ol hydrogenation system was 3-8 times higher than that in a stirred tank reactor under similar conditions.This work proves the feasibility of intensifying the selectivity of hydrogenation process in the RPB reactor.     

“Ethane oxychlorination” over γ-Al2O3 supported CuCl2–KCl–LaCl3

A study on -Al₂O₃ supported CuCl₂/KCl/LaCl₃ for ethane oxychlorination was carried out by means of XRD, XPS,TGA/DTA, BET TEM and ICP. The experimental results indicate that the catalytic properties of the 5 wt,%Cu–6 wt.%K–5 wt.%La/-A1₂O₃ are optimal. This catalyst was studied in more detail and it was found that deactivation of the catalyst was due to carbon deposition and loss of active species of Cu⁺².     

Novel promotional effect of yttrium on Cu–SAPO-34 monolith catalyst for selective catalytic reduction of NOx by NH3 (NH3-SCR)

Cu–SAPO-34 and CuY–SAPO-34 catalysts for NH₃-SCR were prepared by the wet-impregnation method. XRD, UV–vis DRS, ESR and NH₃-TPD results showed that the introduction of Y effectively improved the dispersion of copper species, increased the amount of isolated copper ions and enhanced the acid density. In addition, the activity test, NH₃-TPD and TGA results reflected that the CuY–SAPO-34 catalyst showed better C₃H₆ oxidation activity, lower dropping degree of acid sites after C₃H₆/O₂ treatment and less adsorption of C₃H₆/O₂ than Cu–SAPO-34 catalyst. Therefore, the addition of Y promoted the NH₃-SCR performance and the hydrocarbon (HC) resistance of Cu–SAPO-34 catalyst.