Kinetics of the catalytic oxidation of methanol to formaldehyde

The kinetics of the oxidation of methanol to formaldehyde, over iron molybdate as catalyst, have been studied. The kinetic runs have been performed with a CSTR reactor.The results can be described with a kinetic model derived on the basis of a redox mechanism partially hindered by the adsorption of water. The low temperatures used in the reactor (200–250°C) favour the formation of by-products, as dimetoxymethane, dimethyl ether and methylformate.     

Substrate-mediated enhanced activity of Ru nanoparticles in catalytic hydrogenation of benzene

The impact of carbon substrate-Ru nanoparticle interactions on benzene and hydrogen adsorption that is directly related to the performance in catalytic hydrogenation of benzene has been investigated by first-principles based calculations. The stability of Ru(13) nanoparticles is enhanced by the defective graphene substrate due to the hybridization between the dsp states of the Ru(13) particle with the sp(2) dangling bonds at the defect sites. The local curvature formed at the interface will also raise the Ru atomic diffusion barrier, and prohibit the particle sintering. The strong interfacial interaction results in the shift of averaged d-band center of the deposited Ru nanoparticle, from -1.41 eV for a freestanding Ru(13) particle, to -1.17 eV for the Ru/Graphene composites, and to -1.54 eV on mesocellular foam carbon. Accordingly, the adsorption energies of benzene are increased from -2.53 eV for the Ru/mesocellular foam carbon composites, to -2.62 eV on freestanding Ru(13) particles, to -2.74 eV on Ru/graphene composites. A similar change in hydrogen adsorption is also observed, and all these can be correlated to the shift of the d-band center of the nanoparticle. Thus, Ru nanoparticles graphene composites are expected to exhibit both high stability and superior catalytic performance in hydrogenation of arenes.     

Highly dispersed Pt nanoparticles on nitrogen-doped magnetic carbon nanoparticles and their enhanced activity for methanol oxidation

Pt nanoparticles dispersed nitrogen-doped magnetic carbon nanoparticles (N-MCNPs) were prepared by chemical method, conventional sodium borohydride reduction. Then, those probable applications were evaluated for a support material comparing with Vulcan XC-72 for polymer electrolyte membrane fuel cell. N-MCNPs-supported Pt nanoparticles show a better activity of methanol oxidation reaction compared to Vulcan XC-72-supported one in terms of both mass and electrochemical surface area (ESA) normalized current density. In particular, Pt/N-MCNPs show more enhanced activity based on the mass normalized specific activity rather than ESA normalized activity. For investigation of physical characterizations of Pt/N-MCNPs, and Pt/Vulcan XC-72, X-ray diffraction (XRD), high resolution-transmission electron microscopy (HR-TEM), and X-ray photoelectron spectroscopy (XPS) likes various experiments were performed. Especially, to identify the role of nitrogen in the N-MCNPs for Pt nanoparticles dispersion, specific investigation of N 1s XP spectra with peak deconvolution were performed on N-MCNPs support material of the before and after chemical reduction of Pt nanoparticles.     

Highly dispersed Pt nanoparticles by pentagon defects introduced in bamboo-shaped carbon nanotube support and their enhanced catalytic activity on methanol oxidation

Bamboo-shaped carbon nanotubes (BCNTs), which were synthesized through chemical vapor deposition by using cresol as the carbon source, were explored as Pt catalyst support in comparison with conventional carbon nanotubes (CNTs) and Vulcan XC carbon blacks. The pyrolysis of cresol produced a large amount of pentagon defects introduced in the walls of BCNTs, which could possess higher chemical activity and stronger interaction with metal particles. After a mild purification, the BCNTs exhibited more oxygen-containing functional groups than CNTs, as shown by Fourier transform infrared spectra and cyclic voltammetry. The formed oxygen-containing functional groups as well as the pentagon defects could act as uniform active sites for metal particle loading. By ethylene glycol reduction, highly dispersed Pt nanoparticles with a narrow size distribution of 2-3 nm were easily supported on BCNTs, as shown by transmission electron microscope. The Pt/BCNT catalyst showed higher electro-catalytic activity on the methanol oxidation than the Pt/CNT and Pt/Vulcan XC catalyst, which could be largely ascribed to the highly dispersed Pt nanoparticles due to the introduced pentagon defects in the tube-walls (comparing with Pt/CNT) and the graphitic nanotube network that could provide good electron conduction (comparing with Pt/Vulcan XC).     

Electrodeposition and catalytic activity of palladium powders

Palladium was deposited galvanostatically and potentiostatically from complex chloride solutions at various cds and potentials. The properties of the deposits were studied by a number of methods. The roughness measured with a mechanical profilometer strongly increased upon reaching the limiting cd in agreement with the general theory of the influence of mass transport control on the electrodeposition of metals.The particle size of the Pd-powders obtained above the limiting cd decreased steadily with increasing current density of deposition. In contrast to this, the BET-surface area as well as the catalytic activity (determined by measuring the acceleration of the rate of hydrogenation of cyclohexene) went through a maximum. The latter occurs in the region where the deposit consists of both the α and β H-Pd phases.The metal was deposited on a Pd-electrode as well as on a suspension of active carbon. The maximum catalytic activity was in both cases comparable to that of a non-electrolytic Pd-test catalyst.     

Phosphorus induced hydrothermal stability and enhanced catalytic activity of ZSM-5 in methanol to DME conversion

The change in properties of ZSM-5 samples was achieved by treatment with phosphorus compounds (trimethyl phosphite or phosphoric acid) and the resultant materials were characterized by N₂ adsorption, NH₃-TPD, ²⁷Al, and ³¹P MAS NMR techniques. The phosphorus-treated HZSM-5 (P/ZSM-5) samples exhibited lower acidity, higher hydrothermal stability and improved dimethyl ether (DME) selectivity in methanol conversion when compared to the phosphorus-free HZSM-5. ²⁷Al, and ³¹P MAS NMR results revealed that the added P indeed interacted with the ZSM-5 framework and is responsible for the changes observed in the catalytic properties. The interaction caused the decrease in strong acid sites on one hand and creation of new acid sites (NH₃-TPD) on the other, in P/ZSM-5 samples. The studies indicated the need of optimizing the P loading, where the positive role of P on the catalytic activity was observed to be maximum at P/Al molar ratio of 1.05.     

碳纳米管表面Pd纳米颗粒对甲醇的电催化氧化研究

采用电化学循环伏安法分别在碳纳米管(CNT)和玻碳(GC)电极表面沉积Pd纳米颗粒。扫描电镜(SEM)和XRD分析显示了Pd纳米颗粒均匀分散于碳纳米管表面,而在GC表面则趋向于堆积形成Pd金属薄膜。比较研究了Pd/CNT和Pd/GC电极在碱液中对甲醇的电催化氧化性能,循环伏安结果发现,Pd/CNT对甲醇的催化活性要高于Pd/GC电极;而交流阻抗谱研究发现,Pd/CNT电极对甲醇具有更快的催化氧化速率。另外,不同Pd载量,不同环境温度以及不同甲醇浓度的研究表明,相对于Pd/GC电极,Pd/CNT电极对甲醇的催化氧化具有更高的灵敏度和电化学稳定性。     

Bio-synthesized palladium nanoparticles using alginate for catalytic degradation of azo-dyes

Palladium nanoparticles(PdNPs) were synthesized in a green way using sodium alginate functioning as both reductant and stabilizer. The formation of as-synthesized Pd NPs was supervised by Ultraviolet–visible(UV–Vis)spectroscopy and confirmed by the surface plasmon resonance(SPR) band. The effect of several synthesis factors such as precursor ratio, solution p H, reaction time, and temperature were investigated by the factorial design of experiments in order to optimize the experimental conditions. The optimal synthesis parameters were achieved by heating 1.0 ml of 1.0% sodium alginate(SA), 3.0 ml of 10~(-2) mol·L~(-1) H_2PdCl_4 at 80 °C for a period of 30 min in a neutral reaction medium(pH = 6). High-resolution transmission electron microscope(HRTEM), energy dispersive X-ray(EDX) spectroscopy, selected area electron diffraction(SAED) pattern, X-ray powder diffraction(XRD),and dynamic light scattering(DLS) were used to confirm the uniform spherical shapes and high crystallinity of Pd NPs with average particle size of(2.12 ± 1.42) nm. The SEM images show the distribution of Pd NPs presented among the SA. FTIR spectra indicate that SA is a good capping agent to stabilize Pd NPs for a long time. The catalytic degradation of model azo-dyes such as mono-azo(Cibacron Yellow FN–2R) and di-azo(Cibacron Deep Red S–B) were confirmed the catalytic activity of Pd NPs. The Pd NPs can accelerate the degradation rate by more than 80 and 10 times respectively as confirmed by kinetics constant(k) values.     

介孔氧化锰对甲醛的低温催化氧化

采用硬模板法合成了介孔氧化锰纳米材料,考察了甲醛浓度对甲醛的催化氧化活性的影响。通过X射线衍射(XRD)、透射电镜(TEM)、高分辨透射电镜(HRTEM)等分析手段对合成的介孔材料进行了表征。结果显示,所合成的氧化锰具有很好的有序三维介孔结构,对甲醛具有优异的催化性能。甲醛的初始浓度对催化剂的活性有很大的影响,随着初始浓度的降低,催化剂活性逐渐提高。当甲醛的初始浓度为30 mg/L时,氧化锰催化剂在40℃时即可将甲醛完全降解。对于非贵金属型甲醛降解催化剂,此温度属于较低的。氧化锰优异的催化活性可能与其有序的介孔结构有很大的关系。     

介孔氧化锰对甲醛的低温催化氧化

采用硬模板法合成了介孔氧化锰纳米材料,考察了甲醛浓度对甲醛的催化氧化活性的影响。通过X射线衍射(XRD)、透射电镜(TEM)、高分辨透射电镜(HRTEM)等分析手段对合成的介孔材料进行了表征。结果显示,所合成的氧化锰具有很好的有序三维介孔结构,对甲醛具有优异的催化性能。甲醛的初始浓度对催化剂的活性有很大的影响,随着初始浓度的降低,催化剂活性逐渐提高。当甲醛的初始浓度为30 mg/L时,氧化锰催化剂在40℃时即可将甲醛完全降解。对于非贵金属型甲醛降解催化剂,此温度属于较低的。氧化锰优异的催化活性可能与其有序的介孔结构有很大的关系。     

Adsorption and catalytic reduction of NO with methanol over carbon and carbon-supported catalysts

The effect of various metal additives on the catalytic performance of carbon during the selective reduction of NO with methanol has been studied in the absence and in the presence of gas-phase oxygen. The mechanism of this reaction in the use of carbon-supported catalysts was studied by means of in situ FTIR combined with the measurements of catalytic activity. In the absence of oxygen, NO is adsorbed in a very small amount on the surface of carbon. The reaction of NO with the products of the methanol decomposition, results in the formation of adsorbed isocyanate (NCO) species at 2229 cm⁻¹. Formation of gaseous NH₃ as a product of the reaction between NO and methanol was observed. Oxygen-containing surface functional groups of carbon effectively promotes the reduction of NO with methanol. IR spectroscopic results of this study show that in the presence of O₂ nitric oxide is catalytically oxidized to nitrogen dioxide, which is chemisorbed on the surface of carbon. The surface nitrogen species were identified by FTIR spectroscopy.     

The effect of mass transfer on the catalytic combustion of benzene and methane over palladium catalysts supported on porous materials

Catalytic combustion of benzene and methane over palladium catalysts supported on FAU and MOR zeolites and MCM-41 and KIT-1 mesoporous materials were studied to illustrate the effect of pore size and shape of supports on their catalytic activities. The palladium catalysts supported on mesoporous materials showed high activity and a steep increase in the conversion of benzene with rising temperature. The low activity of palladium catalysts supported on FAU zeolite was ascribed to mass transfer limitation. However, conversion profiles of methane on palladium catalysts were similar, although their supports were different as zeolites and mesoporous materials. The catalytic behavior of palladium catalysts in the combustion of benzene and methane was explained by the diffusion properties of fuels in the pores of zeolites and mesoporous materials.     

Mn-modified HfO2 nanoparticles with enhanced photocatalytic activity

Round shaped Mn-modified HfO₂ nanoparticles were prepared by the Pechini type sol-gel method. The effects of Mn ions on the structure, particle growth, composition, optical properties and photocatalytic performance of HfO₂ particles were investigated. The structure analysis revealed that the insertion of Mn²⁺, Mn³⁺, and Mn⁴⁺ ions inhibited the complete stabilization of tetragonal HfO₂. Also, the decrease of particle size to values lower than 5 nm and the shift of optical band gap from 5.7 to 2.1 eV was obtained as effect of increasing the Mn content. HfO₂ nanoparticles modified with 10 w% Mn exhibited the highest photocatalytic performance, reaching an efficiency of 91.93% in the decomposition of methylene blue, after 120 min of sunlight irradiation. The efficient trapping of photogenerated electrons on the surface of these nanoparticles generated •O₂⁻ radicals, which were the main oxidative species involved in the degradation of the dye. The improved photocatalytic performance of these nanoparticles is then attributable to their increased surface area, suitable photoactivation, and effective transport of photoexcited charge carriers. Based in studies of band gap, valence band position and active species, a mechanism of photodegradation for this photocatalyst was also proposed and discussed.     

Hydrogenation activity and selectivity behavior of supported palladium nanoparticles

Enhancement in activity and selectivity of catalytic hydrogenation using supported nanosize palladium catalyst has been investigated. Pd/C catalyst prepared in the presence of polyvinyl pyrrolidone (PVP) as a stabilizer gave Pd particle size in a narrow range of 3–5 nm. While, evaluating for hydrogenation of 2-butyne-1,4-diol, the rate enhancement was found to be 10 times higher as compared to the conventional (bulk) Pd catalysts. A proper choice of stabilizer (PVP) giving small particle size as well as highly dispersed nature of nano particles were the major factors for such a dramatic enhancement of activity.     

A kinetic study of methanol decomposition catalyzed over plate-type palladium catalyst

A kinetic study of the catalytic methanol decomposition to carbon monoxide and hydrogen has been carried out in the pressure range of methanol up to 8 atm at 200 and 250°C over a palladium catalyst supported on an oxidized aluminum plate. The reaction pathway can be proposed as (i) dissociative adsorption of methanol to methoxyl groups and hydrogen adsorbed on palladium sites, (ii) decomposition of the methoxyl groups to carbon monoxide and hydrogen adsorbed, and (iii) desorption of the surface carbon monoxide and hydrogen species. It is suggested that the second step is rate-determining and the surface hydrogen species enhance the decomposition of the methoxyl groups. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of metal-support interactions on the synthesis of methanol over palladium

The synthesis of methanol and other products from CO and H₂ was studied over Pd catalysts prepared by adsorption of Pd(π-C₃H₃)₂ on MgO, ZnO, La₂O₃, γ-Al₂O₃, SiO₂, TiO₂, and ZrO₂ as well as over a SiO₂-supported Pd catalyst prepared from PdCl₂ and Pd black. Both the activity and selectivity of Pd were affected strongly by the nature of the support and the composition of the Pd precursor. The specific activity for methanol synthesis decreased in the order $\text{Pd}\text{La}{}_2\text{O}{}_3$ ? $\text{Pd}\text{SiO}{}_2$ [derived from PdCl₂] > $\text{Pd}\text{ZrO}{}_2$ > $\text{Pd}\text{ZnO}\text{≈}\text{Pd}\text{MgO}$ > PdTiO₂ > $\text{Pd}\text{Al}{}_2\text{O}{}_3\text{≈}\text{Pd}\text{SiO}{}_2$ [derived from Pd(π-C₃H₅)₂] ? Pd black, while the specific activity for hydrocarbon synthesis decreased in the order $\text{Pd}\text{TiO}{}_2\text{?}\text{Pd}\text{ZrO}{}_2$ > $\text{Pd}\text{La}{}_2\text{O}{}_3$ > $\text{Pd}\text{Al}{}_2\text{O}{}_3\text{≈}\text{Pd}\text{SiO}{}_2$ [derived from PdCl₂] ? $\text{Pd}\text{SiO}{}_2$ [derived from Pd(π-C₃3H₅)₂] ≈ Pd black ? $\text{Pd}\text{MgO}\text{?}\text{Pd}\text{ZnO}$. Dimethyl ether production was observed over four of the catalysts and the activity for formation of this product decreased in the order $\text{Pd}\text{Al}{}_2\text{O}{}_3\text{?}\text{Pd}\text{TiO}{}_2\text{?}\text{Pd}\text{MgO}\text{≈}\text{Pd}\text{ZrO}{}_2$. The effects of support composition on the catalytic properties of Pd are discussed in the light of current ideas concerning metal-support interactions and the acid-base properties of the support.     

Preparation and catalytic properties of composites with palladium nanoparticles and poly(methacrylic acid) microspheres

Palladium (Pd) nanoparticles with different sizes are in situ synthesized by reduction of PdCl₂ with NaBH₄ as reductant in the presence of poly(methacrylic acid) (PMAA)microspheres. The obtained PMAA/Pd composites are characterized by Fourier transform infrared spectra, X‐ray diffraction, and Transmission electron microscopy. The catalytic activity of the PMAA/Pd composites is investigated using a model reaction, that is, reduction of p‐nitrophenol to p‐aminophenol. The reaction shows first‐order kinetics, and the reaction rate increases with increasing reaction temperature, p‐nitrophenol concentration, and loadings of Pd nanoparticles on PMAA microspheres. The PMAA/Pd composites exhibit good stability, ascribing to the Pd nanoparticles stabilized by PMAA microspheres. POLYM. COMPOS., 35:2251–2260, 2014. © 2014 Society of Plastics Engineers     

Structural change of palladium particles supported on cerium oxide in catalytic methanol synthesis

Ultrafine palladium particles supported on cerium oxide by the coprecipitation method effectively catalyzes the methanol synthesis from carbon monoxide and hydrogen, while the catalytic activity increases in the initial stage. The Pd K-edge EXAFS (extended X-ray absorption fine structure) of the catalyst shows that a small part of palladium is still oxidized after the pretreatment with hydrogen at 573 K for 1 h. During the reaction the palladium particles in the catalyst are further oxidized due to the formation of Pd–O–Ce bonding which may stabilize the cationic palladium species being active to the reaction.     

Fabrication of chain-like TiO2 hollow microspheres with enhanced photocatalytic activity

TiO₂ hollow microspheres (TiO₂-HMSs) have attracted much attention due to their low density, high photoreactivity and easy recovery. However, fabrication of TiO₂-HMSs is time-consuming and costly. In this paper, effect of H₂O₂ on the formation of chain-like TiO₂-HMSs was studied using (NH₄)₂TiF₆ as titanium source and urea as neutralizer through a one-pot hydrothermal reaction strategy. The prepared TiO₂-HMSs were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscopy (SEM). The photocatalytic activity of TiO₂-HMSs was evaluated by photocatalytic degradation of an anionic dye X3B under UV irradiation. It was found that the presence of H₂O₂ not only influences the nucleation, but also enhances the hollowing process of TiO₂-HMSs by accelerating the “inside-outside” mass transfer. TiO₂-HMSs prepared in the presence of H₂O₂ showed enhanced photocatalytic activity due to the synergistic effects of well crystallization and hollow structures.     

Sol derived gold–palladium bimetallic nanoparticles on TiO2: structure and catalytic activity in CO oxidation

Bimetallic AuPd catalysts were prepared by deposition of bimetallic aqueous sols formed in different ways: (i) co-reduction of the precursor Au and Pd ions by Na-citrate/tannic acid mixture, (ii) reduction of Au(III) ions onto preformed Pd sol, and (iii) reduction of Pd(II) ions onto a preformed Au sol. The Au/TiO₂ and Pd/TiO₂ samples as references were prepared from their respective sols. The structure of the samples was characterized by XRF, XRD, XPS, TEM and CO chemisorption both in the as-prepared state and after calcination and reduction. The catalytic activities of the calcined/reduced catalysts in the CO oxidation were compared. The presence of bimetallic crystalline phases was evidenced in all three samples both in the as prepared and calcined/reduced states, however, various extents of Pd surface enrichment were determined. The catalytic activity of the bimetallic samples regardless of the preparation method, is about the same as that of the mixture of the monometallic samples. No significant synergism is suggested in the present bimetallic samples.