活性炭改性对用于甲酸分解的Pd/活性炭催化剂的影响

采用磁力搅拌法和水浴振荡法制备应用于甲酸分解的Pd/活性炭(AC)催化剂,研究了活性炭载体改性和制备方法对催化剂分解甲酸性能的影响。采用恒温水浴振荡装置,在80℃水浴中进行甲酸催化分解反应,以甲酸的催化分解率评价催化剂催化活性。结果表明,以经过不同的酸、碱、盐溶液改性后的活性炭为载体采用不同方法制备的Pd/AC催化剂对甲酸的催化分解效果不同,以Na2CO3改性的活性炭为载体采用磁力搅拌法制备的催化剂活性最好,甲酸水溶液的分解率达85%以上,含甲酸的工业废水的分解率达70%。     

含氮中孔碳负载的Au-Pd双金属催化剂在甲酸分解制氢中的催化性能

以SBA-15作为硬模板剂,吡咯作为碳源和氮源,制得的含氮中孔碳作为载体,采用吸附还原法分别制备了单Pd和Au-Pd双金属催化剂,并考察其在甲酸分解制氢反应中的催化性能。结果发现,Au-Pd/N-C比Au-Pd/C催化剂具有更高的甲酸分解活性,这可能是因为N的亲核作用促进了甲酸中H质子的脱除。由于Au-Pd之间的强相互作用,使Au的加入显著提高了Pd/N-C催化剂甲酸分解活性及其抗CO中毒能力,在50℃条件下,分解1 mol·L-1的甲酸初始转换频率(TOF)达到2 221 h-1。     

One-step growth of 3-5 nm diameter palladium electrocatalyst in a carbon nanoparticle-chitosan host and characterization for formic acid oxidation

The electrochemical formation of a palladium nanoparticle catalyst composite material has been investigated. A carbon nanoparticle-chitosan host film deposited onto a carbon substrate electrode has been employed to immobilize PdCl₂ as catalyst precursor. A one-step electrochemical reduction process gave Pd nanoparticles within the chitosan matrix with different levels of loading, on different carbon substrates, and with a reproducible catalyst particle diameter of ca. 3-5 nm. High activity for formic acid oxidation has been observed in aqueous phosphate buffer medium. The oxidation of formic acid has been investigated as a function of pH and maximum catalyst activity was observed at pH 6. When varying the formic acid concentration, limiting behaviour consistent with a “resistance effect” has been observed. A flow cell system based on a screen-printed carbon electrode has been employed to establish the effect of hydrodynamic conditions on the formic acid oxidation. Both increasing the convective-diffusion mass transport rate and increasing the concentration of formic acid caused the oxidation peak current to converge towards the same “resistance limit”. A mechanistic model to explain the resistance effect based on CO₂ flux and localized CO₂ gas bubble formation at the Pd nanoparticle modified carbon nanoparticle-chitosan host film has been proposed.     

Phenol degradation by Fenton's process using catalytic in situ generated hydrogen peroxide

The recent reported pathway using oxygen and formic acid at ambient conditions has been utilized to generate hydrogen peroxide in situ for the degradation of phenol. An alumina supported palladium catalyst prepared via impregnation was used for this purpose. Almost full destruction of phenol was carried out within 6 h corresponding to the termination of 100 mM formic acid at the same time. In addition, a significant mineralization (60%) was attained. A simulated conventional Fenton process (CFP) using continuous addition of 300 ppm H₂O₂ displayed maximum 48% mineralization. Study of different doses of formic acid showed that decreasing the initial concentration of formic acid caused faster destruction of phenol and its toxic intermediates. The catalytic in situ generation of hydrogen peroxide system demonstrated interesting ability to oxidize phenol without the addition of Fenton's catalyst (ferrous ion). Lower Pd content catalysts (Pd1/Al and Pd0.5/Al) despite of producing higher hydrogen peroxide amount for bulk purposes, did not reach the same efficiency as the Pd5/Al catalyst in phenol degradation. The later catalyst showed a remarkable repeatability so that more than 90% phenol degradation along with 57% mineralization was attained by the used catalyst after twice recovery. Higher temperature (45 °C) gave rise to faster degradation of phenol resulting to almost the same mineralization degree as obtained at ambient temperature. Meanwhile, Pd leaching studied by atomic adsorption proved excellent stability of the catalysts.     

Co改性的Pd/C催化剂在转移加氢中的应用研究

通过调整Co和Pd的浸渍顺序制备了不同的钴改性的Pd/C催化剂,考察了催化剂在3,5-二羟基苯甲酸转移加氢制备3,5-二氧代环己烷羧酸反应中的活性。确认先浸渍钴后浸渍钯、并在300℃以氢气还原得到的Co-Pd/C催化剂具有最佳活性,反应转化率和选择性分别达到94.6%和99.5%。对该催化剂以BET、TPR、XRD、SEM、TEM、XPS等手段进行了表征。结果表明,先浸渍的钴占据了活性炭的微孔使最可几孔径由2.72nm增大为3.32nm,并且与一些对反应不利的官能团作用,使后浸渍的钯主要分布在催化剂的大孔中,避免了过多深度加氢副产物的生成。催化剂活性组分为零价的钯,其平均粒径约10nm,以有利于转移加氢的聚集态存在,使催化剂获得了较高的活性和选择性。     

Catalytic transfer hydrogenation of soybean oil methyl ester using inorganic formic acid salts as donors

The hydrogenation of soybean oil methyl esters using aqueous formic acid salts solutions and heterogeneous palladium-on-carbon catalyst was investigated. Complete hydrogenation of the methyl ester was achieved by mixing a concentrated aqueous alkali formate solution with the methyl ester at 80 C in the presence of the catalyst (0.2–0.4% Pd). At the initial stages of the reaction, the selectivity was significantly higher than conventional hydrogenation (hydrogenation under pressure) performed with the same catalyste.Cis-trans isomerization was similar to the behavior of conventional techniques.     

Preparation of high performance Pd catalysts supported on untreated multi-walled carbon nanotubes for formic acid oxidation

Due to the inherent inertness of carbon nanotubes (CNTs), one of the most significant challenges in the preparation of CNT-supported catalysts is achieving a uniform deposition of nanoparticles on the surface of the nanotubes. In this paper, we report on the preparation and characterization of Pd nanoparticles supported on untreated multi-walled carbon nanotubes (MWCNTs), synthesized in the presence of glutamate. The results of Raman spectroscopy revealed that this synthetic procedure does not have a detrimental effect on the surface structure of MWCNTs. Transmission electron microscopy (TEM) measurements indicated that the dispersion of Pd nanoparticles on untreated-MWCNTs in the presence of glutamate were uniform, and a narrow particle size was observed. X-ray diffraction (XRD) patterns indicated that the Pd/MWCNT catalyst possessed a face-centered cubic crystal structure. Cyclic voltammetry and chronoamperometry tests demonstrated that the obtained Pd/MWCNT catalyst displayed superior electrocatalytic activity and stability in formic acid oxidation, as compared to both a Pd/MWCNT catalyst synthesized without glutamate and a Pd catalyst on acid-oxidized MWCNTs, under otherwise identical experimental conditions. These results indicate that the catalyst developed in this study is a superior candidate for direct formic acid fuel cells (DFAFCs).     

Performance characterization of direct formic acid fuel cell using porous carbon-supported palladium anode catalysts

Palladium particles supported on porous carbon of 20 and 50 nm pore diameters were prepared and applied to the direct formic acid fuel cell (DFAFC). Four different anode catalysts with Pd loading of 30 and 50 wt% were synthesized by using impregnation method and the cell performance was investigated with changing experimental variables such as anode catalyst loading, formic acid concentration, operating temperature and oxidation gas. The BET surface areas of 20 nm, 30 wt% and 20 nm, 50 wt% Pd/porous carbon anode catalysts were 135 and 90 m²/g, respectively. The electro-oxidation of formic acid was examined in terms of cell power density. Based on the same amount of palladium loading with 1.2 or 2 mg/cm², the porous carbon-supported palladium catalysts showed higher cell performance than unsupported palladium catalysts. The 20 nm, 50 wt% Pd/porous carbon anode catalyst generated the highest maximum power density of 75.8 mW/cm² at 25 °C. Also, the Pd/porous carbon anode catalyst showed less deactivation at the high formic acid concentrations. When the formic acid concentration was increased from 3 to 9 M, the maximum power density was decreased from 75.8 to 40.7 mW/cm² at 25 °C. Due to the high activity of Pd/porous carbon catalyst, the cell operating temperature has less effect on DFAFC performance.     

Hydrogenation of styrene-butadiene rubber by hydrogen transfer from limonene

The heterogeneous catalytic transfer hydrogenation of styrenebutadiene rubber (SBR) by the use of limonene as hydrogen source and as solvent in the presence of Pd/C as catalyst has been studied. The influence of the heating time on the reduction and on the structure of the donor was studied. Partial hydrogenations of the olefinic bonds of SBR are obtained when a mixture of limonene, SBR and 10% Pd/C is refluxed with vigorous stirring for 50–200 minutes.     

硝酸浓度对水热处理活性炭制备Pd/AC催化剂性能的影响

采用水热硝酸氧化法对活性炭表面基团进行处理,考查了硝酸浓度对活性炭的孔结构、表面含氧基团的影响,对催化剂进行了N_2物理吸附、NH_3-TPD、FTIR、TEM等表征,并评价Pd/AC催化剂催化甲酸分解的性能。结果表明,随着硝酸浓度的提高,活性炭上含氧基团增加,浓度过高会破坏活性炭孔结构,使负载Pd粒子尺寸有所增大,催化剂活性降低。当活性炭在硝酸浓度为1.0 mol·L~(-1),150℃下水热处理4h,负载Pd催化剂的催化活性最好,在甲酸浓度为0.01 mol·L~(-1),90℃反应1 h情况下,甲酸分解率达到92.22%。     

The enhancement effect of MoOx on Pd/C catalyst for the electrooxidation of formic acid

Molybdenum oxide (MoO_x) was added to a Pd/C catalyst using a novel two-step procedure. The enhancement effect of MoO_x on Pd/C catalyst for the electrooxidation of formic acid was verified by electrochemical experiments. Compared to the Pd/C catalyst, the experimental results showed that the addition of MoO_x could significantly enhance the electrocatalytic performances for the electrooxidation of formic acid. Significant improvements in electrocatalytic activity and stability were primarily ascribed to the effect of MoO_x on the Pd catalyst. In addition to the large specific surface area, the hydrogen spillover effect is speculated to have accelerated the electrooxidation rate of formic acid in the direct pathway.     

Effect of pH Value and Temperatures on Performances of Pd/C Catalysts Prepared by Modified Polyol Process for Formic Acid Electrooxidation

The highly active Pd/C catalysts for formic acid electrooxidation have been prepared by a modified polyol process at different pH values of reaction solutions and different reducing temperatures, respectively. Their physical properties have been characterised by energy dispersive analysis of X‐ray, X‐ray diffraction and transmission electron microscopy. Their electrochemical performances for formic acid electrooxidation have been tested by cyclic voltammetry and amperometric i–t curves. The results of physical characterisations show that all the Pd/C catalysts present an excellent face centered cubic crystalline structure. Their particle sizes are decreasing firstly and then increasing with the increasing of the pH values of reaction solutions. The reducing temperatures also markedly affect the Pd particle sizes. And their nanoparticles have narrow size distributions and are highly dispersed on the surface of carbon support, and Pd metal loading in Pd/C catalyst is similar to the theoretical value of 20 wt.%. The results of electrochemical measurements present that the Pd/C catalyst prepared by waterless polyol process at the pH value of 10 and the reducing temperature of 120 °C has the smallest particle size of about 5.6 nm, and exhibits the highest catalytic activity (1172.0 A · g_Pd<?h‐2.85>^–1<?h.8>) and stability for formic acid electrooxidation.     

Nanoporous PdNi/C Electrocatalyst Prepared by Dealloying High‐Ni‐content PdNi Alloy for Formic Acid Oxidation

To improve the electrochemical performance of Pd‐based catalysts for formic acid oxidation, a carbon supported nanoporous PdNi catalyst is prepared by dealloying high‐Ni‐content PdNi alloy nanoparticles in acid solution. The structure of nanoporous PdNi/C catalyst is characterized by X‐ray diffraction, transmission electron microscopy and X‐ray photoelectron spectroscopy. The electrocatalytic results show that the activity of the nanoporous PdNi/C catalyst is higher than that of nonporous Pd/C catalyst. The results demonstrate that the carbon‐supported nanoporous PdNi catalyst has a potential for application in direct formic acid fuel cells.     

Ag单原子负载N改性石墨烯催化CO2加氢制甲酸的理论计算

甲酸是理想的化学储氢介质和有前景的燃料源，CO₂催化加氢制甲酸原子经济性高，是CO₂减排的有效途径之一。通过DFT计算研究了Ag单原子负载N改性石墨烯催化CO₂加氢制甲酸，在4种催化剂上分别考察了3条路线合成产物。结果表明：N的引入提高了催化剂对反应物的吸附能力，降低了反应活化能垒，提高了催化剂的催化活性，为新型2D催化剂催化CO₂加氢制甲酸提供了理论基础。     

ZrC–C and ZrO2–C as Novel Supports of Pd Catalysts for Formic Acid Electrooxidation

The Pd/ZrC–C and Pd/ZrO₂–C catalysts with zirconium compounds ZrC or ZrO₂ and carbon hybrids as novel supports for direct formic acid fuel cell (DFAFC) have been synthesized by microwave‐assisted polyol process. The Pd/ZrC–C and Pd/ZrO₂–C catalysts have been characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), energy dispersive analysis of X‐ray (EDAX), transmission electron microscopy (TEM), and electrochemical measurements. The physical characteristics present that the zirconium compounds ZrC and ZrO₂ may promote the dispersion of Pd nanoparticles. The results of electrochemical tests show that the activity and stability of Pd/ZrC–C and Pd/ZrO₂–C catalysts show higher than that of Pd/C catalyst for formic acid electrooxidation due to anti‐corrosion property of zirconium compounds ZrC, ZrO₂, and metal–support interaction between Pd nanoparticles and ZrC, ZrO₂. The Pd/ZrC–C catalyst displays the best performance among the three catalysts. The peak current density of formic acid electrooxidation on Pd/ZrC–C electrode is nearly 1.63 times of that on Pd/C. The optimal mass ratio of ZrC to XC‐72 carbon is 1:1 in Pd/ZrC–C catalyst with narrower particle size distribution and better dispersion on surface of the mixture support, which exhibits the best activity and stability for formic acid electrooxidation among all the samples.     

Effects of iron-tetrasulfophthalocyanine on the catalytic activities of Pt/C,PtRu/C,and Pd/C catalysts in a multi-anode direct formic acid fuel cell

This paper reports a systematic study of the effects of a promoter, iron-tetrasulfophthalocyanine (FeTSPc), on the catalytic activities of carbon supported Pt, PtRu, and Pd catalysts (Pt/C, PtRu/C, and Pd/C) for formic acid oxidation. A multi-anode direct formic acid fuel cell (DFAFC) was used to compare the effects on each catalyst of adding FeTSPc to the fuel stream. The FeTSPc significantly enhanced the activity of the Pt/C catalyst, but had little effect on the PtRu/C catalyst. The activity of the Pd/C catalyst was inhibited by the FeTSPc. A FeTSPc modified Pt/C was also evaluated in a conventional 5 cm² DFAFC.     

Hydrogen storage properties of Pd nanoparticle/carbon template composites

Theoretical studies predict improved hydrogenation properties for hybrid carbon/metal composites. The hydrogen storage capacity of ordered porous carbon containing Pd clusters was measured. The C/Pd composite was obtained by chemical impregnation of an ordered porous carbon template (CT) with a H₂PdCl₄ solution followed by a reduction treatment. 10 wt.% of palladium clusters were introduced in the carbon porosity; the Pd clusters (2 nm in size) being homogeneously distributed. Thermodynamic hydrogenation properties of both Pd-free CT and the Pd-10 wt.% CT composite have been determined by hydrogen isotherm sorption measurements and thermal desorption spectroscopy (TDS) analysis. The introduction of the palladium into the carbon matrix does not increase the hydrogen storage capacity at 77 K and 1.6 MPa, since here the hydrogen uptake is being attributed to physisorption on the carbon. However, at room temperature and moderate pressure (0.5 MPa), the filling of the CT with 10 wt.% nanocrystalline Pd results in an hydrogen uptake eight times larger than that of the Pd-free CT. After the second cycle, a good reversibility is observed. TDS measurements confirm that the sharp increase of the hydrogen uptake is due to the presence of the Pd clusters in the carbon porosity.     

Aspects of carbon dioxide utilization

Carbon dioxide reacts with hydrogen, alcohols, acetals, epoxides, amines, carbon–carbon unsaturated compounds, etc. in supercritical carbon dioxide or in other solvents in the presence of metal compounds as catalysts. The products of these reactions are formic acid, formic acid esters, formamides, methanol, dimethyl carbonate, alkylene carbonates, carbamic acid esters, lactones, carboxylic acids, polycarbonate (bisphenol-based engineering polymer), aliphatic polycarbonates, etc. Especially, the productions of formic acid, formic acid methyl ester and dimethylformamide with a ruthenium catalyst; dimethyl carbonate and urethanes with a dialkyltin catalyst; 2-pyrone with a nickel-phosphine catalyst; diphenyl carbonate with a lead phenoxide catalyst; the alternating copolymerization of carbon dioxide and epoxides with a zinc catalyst has attracted attentions as the industrial utilizations of carbon dioxide. The further development of these production processes is expected.     

钯基催化剂应用于甲酸电氧化反应的研究进展

甲酸是一种很有前途的化学储氢材料,可作为低温液体燃料电池的直接燃料。钯基催化剂作为直接甲酸燃料电池（DFAFC）阳极材料,对甲酸氧化具有良好的催化活性,能克服一氧化碳的毒化,在甲酸电化学氧化反应中主要按直接途径进行。降低贵金属含量、提高催化活性、提升稳定性是当前钯基催化材料研究领域的主要方向。主要介绍了当前研究中钯催化剂对甲酸电氧化的催化机理,综述了近5 a的钯合金催化剂制备、特殊形貌控制、碳负载对甲酸氧化活性增强的研究,对钯基催化剂的持续开发具有实际应用意义。     

Vapour phase hydrogenation of phenol over Pd/C catalysts: A relationship between dispersion,metal area and hydrogenation activity

A series of palladium supported on activated carbon catalysts, with Pd varying from 0.5 to 6.0 wt%, were prepared via wet impregnation method using PdCl₂ · xH₂O as a precursor salt. The dried samples were further reduced at 573 K in hydrogen and characterized by CO adsorption at room temperature in order to determine the dispersion, metal area and particle size. The catalysts were tested for vapour phase phenol hydrogenation in a fixed-bed all glass micro-reactor at a reaction temperature of 453 K under normal atmospheric pressure. The decrease in metal surface area as well as dispersion with corresponding increase in turn-over frequency (TOF) against palladium loadings suggest the unusual inverse relationship that exist between Pd dispersion and phenol hydrogenation activity over Pd/carbon catalysts. The stability of TOF at larger crystallite size indicates that phenol hydrogenation is less sensitive reaction especially beyond 3 wt% of Pd content. It is evident from the results that structural properties of the catalysts strongly influence the availability of Pd atoms on the surface for CO chemisorption and hence for phenol hydrogenation. A comparison between selectivity and product yield of the reaction against overall phenol conversion indicates that changes in reaction selectivity for cyclohexanone or cyclohexanol is independent of phenol conversion level and either of the product is not formed at the cost of another. The stability of the catalysts with reaction time suggests that coke formation on the surface of the catalyst is less significant and the formation of cyclohexanone remains almost total even at higher reaction temperatures.