Preparation of palladium-based catalyst by plasma-assisted atomic layer deposition and its applications in CO_(2) hydrogenation reduction

Supported Pd catalyst is an important noble metal material in recent years due to its high catalytic performance in CO_(2)hydrogenation.A fluidized-bed plasma assisted atomic layer deposition(FP-ALD) process is reported to fabricate Pd nanoparticle catalyst over γ-Al_(2)O_(3)or Fe_(2)O_(3)/γ-Al_(2)O_(3)support,using palladium hexafluoroacetylacetonate as the Pd precursor and H_(2)plasma as counter-reactant.Scanning transmission electron microscopy exhibits that highdensity Pd nanoparticles are uniformly dispersed over Fe_(2)O_(3)/γ-Al_(2)O_(3)support with an average diameter of 4.4 nm.The deposited Pd-Fe_(2)O_(3)/γ-Al_(2)O_(3)shows excellent catalytic performance for CO_(2)hydrogenation in a dielectric barrier discharge reactor.Under a typical condition of H_(2)to CO_(2)ratio of 4 in the feed gas,the discharge power of 19.6 W,and gas hourly space velocity of10000 h^(-1),the conversion of CO_(2)is as high as 16.3% with CH_(3)OH and CH4selectivities of 26.5%and 3.9%,respectively.

Highly reactive and reusable heterogeneous activated carbons-based palladium catalysts for Suzuki-Miyaura reaction

Suzuki-Miyaura reaction of aryl halides with phenylboronic acid using a heterogeneous palladium catalyst based on activated carbons(AC) was systematically investigated in this work. Two different reaction modes(batch procedure and continuous-flow procedure) were used to study the variations of reaction processing. The heterogeneous catalysts presented excellent reactivity and recyclability for iodobenzene and bromobenzene substrates in batch mode, which can be attributed to stabilization of Pd nanoparticles by the thiol and amino groups on the AC supports. However, significant dehalogenation in the reaction mixture and Pd leaching from the heterogeneous catalysts were observed in continuous-flow mode.This unique phenomenon in continuous-flow mode resulted in a dramatic decline in reaction selectivity and durability of heterogeneous catalysts comparing with that of batch mode. In addition, the heterogeneous Pd catalysts with thiol-and amino-modified AC supports exhibited different reactivity and durability in batch and continuous-flow mode owing to the difference of interaction between Pd species and AC supports.

Facile molybdenum and aluminum recovery from spent hydrogenation catalyst

Industrial catalyst waste has emerged as a hazardous pollutant that requires safe and proper disposal after the unloading process.Finding a valuable and sustainable strategy for its treatment is a significant challenge compared to traditional methods.In this study,we present a facile method for the recovery of molybdenum and aluminum contents from spent Mo-Ni/Al_(2)O_(3) hydrogenation catalysts through crystallization separation and coprecipitation.Furthermore,the recovered molybdenum and aluminum are utilized as active metals and carriers for the preparation of new catalysts.Their properties were thoroughly analyzed and investigated using various characterization techniques.The hydrogenation activity of these newly prepared catalysts was evaluated on a fixed-bed small-scale device and compared with a reference catalyst synthesized from commercial raw reagents.Finally,the hydrogenation activity of the catalysts was further assessed by using the entire distillate oil of coal liquefaction as the raw oil,specifically focusing on denitrogenation and aromatic saturation.This work not only offers an effective solution for recycling catalysts but also promotes sustainable development.

Palladium nanoparticles in cross-linked polyaniline as highly efficient catalysts for Suzuki-Miyaura reactions

Palladium nanoparticles supported on cross-linked polyaniline with bulky phosphorus ligands were developed.These catalysts showed high efficiency in the Suzuki-Miyaura reaction of aryl chlorides and bromides with phenylboronic acids.Aryl chlorides and bromides with functional groups,such as CN,MeO,CHO,MeCO and NO_2,were converted to the corresponding biphenyls in high yields with catalyst loading.Additionally,the catalysts combined high activity with good reusability;they could be used at least five times for the Suzuki-Miyaura coupling reaction.

Complete Oxidation of Methane over Palladium Supported on Alumina Modified with Calcium,Lanthanum,and Cerium Ions

The activity and thermal stability of Pd/Al2O3 and Pd/（Al2O3＋MOx） （M=Ca, La, Ce） palladium catalysts in the reaction of complete oxidation of methane are presented in this study. The catalyst supports were prepared by sol-gel method and they were dried either conventionally or with supercritical carbon dioxide. Then they were impregnated with palladium nitrate solution. The catalysts with unmodified alumina had a high surface area. The activity and thermal stability of the aluminasupported catalyst was also very high. The introduction of calcium, lanthanum, or cerium oxide into alumina support caused a decrease of the surface area in the way dependent on the support precursor drying method. These modifiers decreased the activity of palladium catalysts, and they required higher temperatures for the complete oxidation of methane than unmodified Pd/Al2O3. The improvement of the palladium activity by lanthanum and cerium support modifier was observed only at low temperatures of the reaction.

Synthesis and Performance of Mesoporous Phosphotungstic Acid/Alumina Composite as a Novel Oxidative Desulfurization Catalyst

A series of mesoporous phosphotungstic acid/alumina composites （HPW/Al_2O_3） with various HPW contents were synthesized by evaporation-induced self-assembly method. These composites were characterized by nitrogen adsorption-desorption, TEM, FTIR, and UV-vis, and were tested as catalysts in oxidation desulfurization of model fuel composed of dibenzothiophene （DBT） and hydrocarbon, using H202 as the oxidant. These composites exhibited high activity in catalytic oxidation of DBT in model fuel and good reusing ability. The best performance was achieved by using the mesoporous HPW/Al_2O_3 with 15wt% HPW content, which resulted in a DBT conversion of 98% after 2 h reaction at 343 K, and it did not show significant activity degradation after 3 recycles. Characterization results showed that the mesoporous structure of alumina and the Keggin structure of HPW were preserved in the formed composite. These results suggested that HPW/ Al_2O_3 could be a promising catalyst in oxidative desulfurization process.

Influence of CeO_2 and La_2O_3 on properties of palladium catalysts used for emission control of natural gas vehicles

Pd/YZ-Al2O3 （Y and Zr modified Al2O3, and hereafter, labelled as A1） catalysts with 4 wt% additive CeO2 and/or La2O3 were prepared and characterized by X-ray photoelectron spectroscopy （XPS）, NO-temperature programmed desorption （NO-TPD）, Nz-adsorption/desorption （Branauer-Emmet-Teller BET method）, X-ray diffraction （XRD） and CO-chemisorption. Catalytic activities for CH4, CO and NO conversion were tested in a gas mixture simulated the emissions from natural gas vehicles （NGVs） operated under stoichiometric conditions. The results indicated that all catalysts exhibited excellent catalytic performances for CH4 and CO oxidation and the promoting effect of CeO2 or La2O3 was significant for NO conversion. XPS results showed that the electron density around Pd was increased by CeO2 and/or La2O3, the binding energy of Pd 3d decreased as the order： Pd/Al 〉 Pd/Ce/Al 〉 Pd/La/Al 〉 Pd/CeLa/Al. The electron-rich Pd showed Rh-like catalytic properties which exhibited good activity for the reduction of NO. NO-TPD results showed that the addition of CeO2 and/or La2O3 increased NO adsorption on surface, and promoted the conversion of NO.

Oxidative Esterification of Methacrolein to Methyl Methacrylate over Supported Palladium Catalyst

Supported palladium catalysts, which were used in the oxidative esterification of methacrolein to methyl methacrylate, have been prepared with different carriers and Pd precursors. Experimental results revealed that Pd catalysts with r-Al2O3 support and Na2PdC14 precursor showed good performance. Pd catalyst modified with Pb and Mg indicated that Pd-Mg bimetallic catalyst exhibited considerably higher activity and Pd-Pb exhibited both higher activity and selectivity. 92.27% methacrolein conversion and 90.57% methyl methacrylate selectivity were obtained on Pd-Pb-Mg catalyst.

Methane combustion over palladium catalyst within the confined space of MFI zeolite

Isolated cationic Pd species encapsulated in MFI zeolite,i.e.,Pd@MFI,have been successfully prepared via in situ hydrothermal route followed by oxidative treatment.The as-prepared Pd@MFI samples are investigated as promising catalysts in the reaction of methane combustion.Typically,Pd@H-ZSM-5 shows remarkable activity in methane catalytic combustion with a low apparent activation energy value of 70.7 kj/mol as well as good catalytic stability even in excess water vapor.Detailed characterization results demonstrate the strong interaction between Pd sites and zeolite framework in Pd@ZSM-5 and the efficient stabilization of isolated Pd sites by zeolite thereof.Spectroscopy analyses reveal that the presence of BrΦnsted acid sites is beneficial to methane adsorption and its subsequent activation on adjacent Pd sites,constructing cooperation between Bronsted acid sites and Pd sites within the confined space of MFI zeolite toward high-efficiency methane catalytic combustion.The reaction mechanism of methane combustion catalyzed by Pd@H-ZSM-5 model catalyst is finally discussed.

Chitosan-immobilized Palladium Complex: a Green and Highly Active Heterogeneous Catalyst for Heck Reaction

A green heterogeneous catalyst for Heck reaction-chitosan-immobilized palladium complex was prepared. The catalyst exhibits high activity and stereoselectivity under the moderate reaction conditions. The catalyst can be separated easily from the reaction mixture and reused after washing. Under the suitable reaction conditions, the cross-coupling of iodobenzene (ArI) with acrylic acid (AA) or acrylate can be achieved 93.3% or 99% yield of trans-cinnamic acid or trans-cinnamic ester.

Macroporous magnetic poly(GMA-EGDMA-DVB) microspheres supported palladium complex as an efficient catalyst for Heck reaction

Macroporous magnetic poly(GMA-EGDMA-DVB) microspheres synthesized by suspension polymerization were used as supports for palladium catalyst.The results showed the novel magnetic catalyst can promote Heck reaction of aryl halides with acrylic acid efficiently without an inert atmosphere.In addition,the novel catalyst can be conveniently recovered by applying an external magnet and reused at least five times without significant loss of its activity.

Effect of Lanthanum on Methanol Fuel Exhaust Deep Oxidation over Palladium Catalyst

The performance of deep oxidation of methanol on supported Pd catalyst was exami ned by a chromatograph-micro-reactor. The results show that the add ition of La into γ-Al 2O 3 support can affect greatly the performance of t he Pd catalyst. In the absence of CO, La can decrease the content of oxygen-c ontaining intermediate, although La can not lower the light-off temperature of methanol oxidation. In the presence of CO, La can lower the light-off tem perature, decrease the amount of CO adsorption, and weaken evidently 'CO inhibi tion' to the oxidation of methanol. By XPS technique, it is shown that La modi fies the electronic structure of Pd, which attributes to the modifications of th e catalytic performance.

Hydrothermal treatment of metallic-monolith catalyst support with self-growing porous anodic-alumina film

Metallic-monolith catalyst support with self-growing porous anodic alumina(PAA)film was prepared by anodizing Al plate.The effect of hydrothermal treatment(HTT)on the crystalline state and textural properties of PAA film was investigated by XRD,BET,SEM and TG.The HTT treatment above 50°C and the subsequent calcination above 300°C could convert the amorphous skeleton alumina intoγ-alumina and increase the specific surface area(SBET).However,SEM images showed the HTT modification was a non-uniform process along the thickness of PAA film.The promotion effect of HTT on SBETwas non-linear,and the slope of SBETgradually decreased with the HTT temperature or time increased.The limited HTT effect should be attributed to a changed pore structure caused by an unfavorable pore sealing limitation.Pore widening treatment(PWT)before HTT could break the pore sealing limitation,because of the reduced internal diffusion resistance of hydrothermal reaction.The synergistic combination of PWT and HTT developed a PAA support with a large SBETcomparable to commercialγ-alumina.In the catalytic combustion of toluene,the Pt-based catalyst prepared by using the PWT and HTT comodified PAA support gave higher Pt dispersion and more favorable catalytic activity than that treated by HTT alone.The presence of a bimodal pore structure was suggested to be a decisive reason.

Research Progress of Palladium Catalysts for Methane Combustion

Recent research progress and development of the palladium catalysts for methane combustion are described in this study.The influence of active species,precursor,solvent,preparation methodologies,support and dopant on the catalytic activity and thermal stability of the palladium catalysts was discussed.Results of deactivation and poisoning of palladium catalysts were analyzed.Furthermore,possible kinetic models and reaction mechanism were indicated for Pd catalysts.

Preparation of Alumina Abrasion-Resistant Ceramic Grinding Ball with Spent FCC Equilibrium Catalyst

The chemical composition, structure and thermal stability of the spent FCC equilibrium catalyst from an oil refinery were characterized by XRD, FT-IR, DTA-TG, BET, complete chemical analysis, SEM, and XRF. The spent FCC equilibrium catalyst, clay, barium carbonate, and talc were used as the main raw materials to prepare the alumina abrasion-resistant ceramic balls to be used in the powder grinding mill for manufacture of architecture tiles. The results showed that after proper formulation study, the spent FCC equilibrium catalyst could replace industrial alumina to prepare high performance grinding balls. Meanwhile, the various performance indices of the grinding ball could meet the quality standard for similar products, and additionally, the energy saving effect was achieved in the operation of the grinding section, resulting in a successful comprehensive utilization of solid wastes.

Synthesis and characterization of multiwall carbon nanotubes/alumina nanohybrid-supported cobalt catalyst in Fischer-Tropsch synthesis

Multiwall carbon nanotubes （MWNTs） and alumina are combined to give a new type of nanohybrid for Fisher-Tropsch synthesis （FTS） catalyst support. Alumina nano-particles （10 wt%） were introduced directly on functionalized MWNTs by a modified sol-gel method. Microstructure observations show that alumina particles were homogeneously dispersed on the inside and outside of modified MWNTs surfaces. 15 wt% cobalt loading catalysts were prepared with this nanohybrid and γ-alumina as a reference, using a sol-gel technique and wet impregnation method respectively. These catalysts were characterized by TEM, XRD, N2-adsorption, H2 chemisorption and TPR. The deposition of cobalt nanoparticles synthesized by sol-gel technique on the MWNTs nanohybrid shift the reduction peaks to a low temperature, indicating higher reducibility for uniform cobalt particles. Nanohybrid also aided in high dispersion of metal clusters and high stability and performance of catalyst. The proposed MWNTs nanohybrid-supported cobalt catalysts showed the improved FTS rate （gHc/（gcat.min））, CO conversion （%）, and water gas shift rate （WGS）（gcoz/（gcat.h）） of 0.012, 52, and 30E-3, respectively, as compared to those of 0.007, 25, and 18E-3, respectively, on the γ-alumina-supported cobalt catalysts with the same Co loading.

In-Situ FTIR Study on Effect of Lathanum on Oxidation Mechanism of Methanol Automobile Exhaust on Supported Palladium Catalyst

The performance of severe oxidation of methanol on 0.1%Pd supported on alumina was studied by a combined device of chromatograph-micro reactor. The results show that the addition of La into γ-Al 2O 3 as support can affect the performance of Pd catalyst greatly. By using Pd catalyst containing La in methanol oxidation, though, the ignition temperature is not lower than that by using Pd catalyst, the presence of La does suppress the formation of oxygenic intermediates. The results by in-situ FTIR show that the presence of La in the support affects the adsorbed species and hence the mechanism of severe oxidation of methanol on Pd catalyst.

Solvent-free synthesis of alumina supported cobalt catalysts for Fischer–Tropsch synthesis

A novel mechano-synthesis method has been elaborated in this work for the design of efficient cobalt-based Fischer–Tropsch catalysts. The process aims to reduce the total number of steps involved in the synthesis of solid catalysts and thus to avoid relevant toxic solutions generated during the catalyst preparation. The mechano-synthesis of the Co/Al2O3catalyst was processed in a low-energy vibratory micro mill and high energy planetary ball mill. Porous spherical γ-aluminas (1860 µm and 71 µm mean particle diameter) were used in this work as host compounds. Co3O4(3 µm mean particle diameter) has provided guest particles for mechano-synthesis. The catalysts were characterized by textural (surface area, porosity and particle size) and structural analyses (X-ray diffraction, TPR, SEM-EDX and microprobe). The microprobe images show deposition of Co3O4on the surface of the alumina and indicated no Co3O4diffusion inside the alumina pores. SEM-EDX mapping illustrated that cobalt coating tended to occur on surface of rounded shape of cracked alumina fragments. After milling, the crystallite size of Co3O4decreased to 15 nm from 30 to 50 nm. The TPR profiles indicated very low concentrations of inactive cobalt aluminate mixed compounds which are usually produced during the catalyst preparation by impregnation. In Fischer–Tropsch synthesis, the catalysts prepared using mechano-synthesis methods showed catalytic performance comparable to the catalysts prepared by impregnation. © 2016 Science Press

Novel Oxygen Storage Components Promoted Palladium Catalysts for Emission Control in Natural Gas Powered Engines

A three-way catalyst comprised novel oxygen storage components for emission control in natural gas powered engines was prepared. The addition of novel oxygen storage components to the Pd/γ-Al2O3 catalysts resulted in improved activities of the fresh and aged catalyst by lowering the light-off temperature for methane in natural gas engines exhaust.

Fischer-Tropsch Synthesis over Alumina- Supported Cobalt-Based Catalysts: Effect of Support Variables

Different kinds of aluminum precursors were obtained from precipitating ammonium bicarbonate, ammonium carbonate, and saturated ammonium bicarbonate, then, boehmite (AlO(OH)), ammonium alumina carbonate hydroxide (AACH) and their mixture were obtained, and then, different kinds of alumina were obtained after calcination. Three catalysts supported on the different alumina were obtained via impregnating cobalt and ruthenium by incipient wetness. The effects of different precipitants on composition of precursors were?studied by XRD, FTIR, and TGA. The property and structure of alumina were studied by XRD and BET. The supported catalysts were studied by characterizations of XRD and H2-TPR, and the catalytic performance for Fischer-Tropsch synthesis (FTS) were evaluated at a fix-bed reactor. The relations among the composition of precursors, the property of alumina and the catalytic performance of supported catalysts were researched thoroughly.