Influence of Pd Precursor and Method of Preparation on Hydrodechlorination Activity of Alumina Supported Palladium Catalysts

A series of alumina supported Pd catalysts were prepared by the novel deposition-precipitation method adopting the chloride precursor (DP-Cl) of Pd and varying the metal content from 0.25 to 1.0 wt%. The catalytic properties of prepared catalysts were studied by various characterization techniques such as N₂ adsorption, CO chemisorption, TPR, XRD, XPS, and TEM techniques. The activity and stability of the catalysts were evaluated for the gas phase hydrodechlorination (HDC) of chlorobenzene operating at atmospheric pressure. At 1 wt% of Pd the catalyst showed higher chlorobenzene conversion with good stability when tested for a period of 25 h, whereas the other catalysts exhibited a loss in activity with time. In order to elucidate the exceptional activity and stability of this catalyst, a few more catalysts with 1 wt% Pd were prepared by impregnation technique and also using a non-chloride precursor, palladium nitrate. The 1 wt% DP-Cl catalyst again was found to be the best among the others. The activity and stability of the DP-Cl catalyst was also found to be superior to two low-dispersed catalysts, each with 10 wt% Pd, prepared by conventional impregnation method using the chloride and nitrate as the precursors. The characterization results reveal that the high activity and stability of the DP-Cl catalyst is related to the formation of electron deficient Pd species and its stabilization in the octahedral vacancies of alumina.     

对称四取代钯酞菁的合成及其对氯苯气相加氢脱氢的催化作用

1 INTRODUCTION Catalytic hydrodechlorination is an elegant reaction for disposal of environmentally hazardous chlorocarbons,such as chloro-benzene[1].Development of a new catalyst with excellent stability is necessary due to the deactivation of supported noble metal catalysts[1].However the modification of catalytic properties of catalysts in hydrodechlorination reaction by introducing stable ligands to noble metals has been the least studied.Here the synthesis of Pd(Ⅱ) 2,9,16,23-symetrically tetrasubstituted phthalocyanines PdPTX4 (where X=-H,-NO2,-NH2 respectively) from phthalimide derivatives is reported,and their application as catalysts in hydrodechlorination of chlorobenzene,which is a representative environmentally hazardous materials is discussed.     

Hydrodechlorination of Chlorobenzene Over Ni2P/SiO2 Catalysts: Influence of Ni2P Loading

The influence of Ni₂P loading on the properties of Ni₂P/SiO₂ catalysts was investigated by means of N₂ adsorption–desorption, X-ray diffraction, H₂ and NH₃ temperature-programmed desorption, CO chemisorption, inductively coupled plasma atomic emission spectroscopy and activity evaluation for the hydrodechlorization of chlorobenzene. It was found that increasing Ni₂P loading results in the decrease of Ni₂P dispersion. Higher P/Ni ratio occurs in the catalysts with lower Ni₂P loadings, indicating that smaller Ni₂P crystallites may more strongly interact with surplus P. We suggest that the acid amount of the Ni₂P/SiO₂ catalyst is related to the exposed Ni sites and P-OH groups, while Brönsted acidity of P-OH groups facilitates hydrogen spillover. Increasing Ni₂P loading is favorable to the catalyst activity, while this effect is not obvious when the Ni₂P loading is greater than 9.6 wt%. Apart from the metallic property of Ni₂P phase and spilt-over hydrogen species, we propose that the acidity and the role of P in activating reactants should be considered for the catalyst performance.     

Hydrodechlorination of 1,1-Dichlorotetrafluoroethane on Supported Palladium Catalysts. A Static-Circulation Reactor Study

Supported palladium catalysts were studied in CF₃CFCl₂ hydrodechlorination at 100°C using a static-circulation system. In order to minimize catalyst's deactivation a large excess of hydrogen was employed (H₂/CF₃CFCl₂ ratio 54/1). In spite of this precaution significant inhibition of the process occurred, associated with blocking palladium surface by hydrogen chloride species. Differences in the catalytic behavior of alumina-supported and unsupported palladium are discussed. A mild dependence between the catalytic activity and Pd dispersion was found. The Pd/Al₂O₃ catalyst characterized by low metal dispersion was more active than highly dispersed catalysts, showing the overall activity and selectivity to CF₃CFH₂ comparable with those observed by other authors for palladium single crystals. It is speculated that the most active sites for hydrodechlorination are plane atoms, whereas low coordination sites (on edges and corners of metal crystallites) are less suitable.     

Acetylene and Ethylene Hydrogenation on Alumina Supported Pd-Ag Model Catalysts

Adsorption and co-adsorption of ethylene, acetylene and hydrogen on Pd-Ag particles, supported on thin alumina films, have been studied by temperature programmed desorption (TPD). The TPD results show that adding of Ag to Pd suppresses overall hydrogenation activity but increases selectivity towards ethylene, i.e. similar to that observed on real catalysts. The results are rationalized on the basis of a complex interplay between surface and subsurface hydrogen species available in the system, whereby the latter species are the most critical for total hydrogenation of acetylene to ethane.     

CNTs负载双金属Pd-Fe非晶态催化剂加氢脱卤性能初探

以CNTs为载体制备的Pd-Fe双金属非晶态催化剂用于氯代硝基苯的加氢脱卤反应。对该催化剂在超临界CO2中的催化活性进行了评价。实验结果证明,该催化剂在实验条件下具有较好的加氢脱氯活性。用XRD和SEM技术对该催化剂的结构和形貌进行了表征,并初步探讨了该催化剂的加氢脱卤机理。     

助剂对Pd/AC催化剂催化三氟氯乙烯加氢脱氯的影响

采用等体积浸渍法制备了Cu-Pd/AC和K-Pd/AC催化剂,分别考察了Cu和K助剂添加量对三氟氯乙烯加氢脱氯生成三氟乙烯的反应性能的影响,并采用N_2-物理吸附、X射线粉末衍射(XRD)测试、透射电镜(TEM)和H_2-程序升温还原(TPR)等对催化剂进行表征。结果表明:加入助剂Cu,其与Pd形成Pd-Cu合金,抑制催化剂的加氢性能,从而降低催化剂反应活性;加入助剂K,其改变了Pd的电子结构,增强了Pd的电子云密度,使Pd活化H的能力增强,从而提高催化剂的活性。助剂K质量分数为3%的催化剂,在250℃下,具有较好的催化活性,三氟氯乙烯的转化率可达90%左右,三氟乙烯的选择性可达85%左右。     

Carbon Formation on Unsupported and Supported Nickel Catalysts

Studies have been made of the kinetics of carbon deposition on supported nickel catalysts used for steam reforming. Comparison with results obtained with nickel foils show that the support has little effect on the rate of deposition, except that hydrogen did not affect the kinetics of the process on supported catalysts. This is explained in terms of the initial production of nickel crystallites, which are then carried with the growing carbon by a process of diffusion of carbon through the nickel. Calculations show that this diffusion process may well involve the formation of an intermediate carbide.     

结构化纳米碳纤维载体的制备与应用

研究了通过气相沉积法裂解甲烷在TiO2表面生长纳米碳纤维层,制备具有中孔孔径结构的结构化纳米碳纤维的方法。利用SEM-EDS和BET对该载体进行了表征。结果发现,该结构化纳米碳纤维载体的纳米碳纤维层厚度1.5～2.0μm,比表面积60.3 m2/g,其中外表面积为51.1 m2/g,只有很少的内表面积;平均孔径为5nm。在肉桂醛加氢反应中,该载体负载Pd催化剂能明显降低内扩散对反应选择性的影响,肉桂醛转化率低于56%时,氢化肉桂醛选择性达98%,明显高于常规活性炭负载型Pd催化剂。     

Hydrodechlorination Reactions of CCl4 Over HZSM-5- and HY-Supported Pt and Pd Catalysts

The hydrodechlorination reactions of CCl₄ have been studied over Pt/HZSM-5, Pt/HY, Pd/HZSM-5 and Pd/HY under hydrogen atmosphere in the 393?C673?K temperature range in a pulse microreactor. The catalysts were prepared by impregnation and were characterised by various physico-chemical means. It has been found that all catalysts were active in the partial to full dechlorination reactions. Typically, over the Pt-containing catalysts methane was the major dechlorinated product, while it was ethane over the Pd-containing catalysts. This latter product predominated over the Pd/HZSM-5 and the quantities of the di- and trichlorinated products were minimal and the monochlorinated one was not formed at all. Phosgene formed was the indication of the partial destruction of the support being more serious for the HY-supported ones.     

Improved Activity and Stability of Chlorobenzene Oxidation Over Transition Metal-Substituted Spinel-Type Catalysts Supported on Cordierite

Catalysis Letters - Industrial catalysts usually encounter great challenges in Cl· deactivation, toxic by-products generation, and stability with a long running operation for catalytic...     

Fe-Mn-CeOx/AC@CNTs催化剂低温协同去除NO和氯苯

以活性炭@碳纳米管（AC@CNTs）为载体，通过浸渍法制备了Mn-CeOx/AC@CNTs催化剂，并考察了铁物种的引入对Mn-CeOx/AC@CNTs催化剂同时去除一氧化氮（NO）和氯苯（CB）活性的影响。利用SEM、XRD、Raman、FTIR、XPS、H2-TPR等方法对催化剂的理化性质进行了表征。结果表明，Mn物种进入CeO2的晶格中形成Mn-Ce固溶体促进氧空位的生成，而催化剂表面存在丰富的C—H基团和含氧基团有利于提高催化剂的低温催化活性。与Mn-CeOx(1:7)/AC@CNTs（n(Mn):n(Ce)=1:7）催化剂相比，Fe-Mn-CeOx(1:7)/AC@CNTs催化剂表面吸附氧的含量和酸位点数量显著增加，使其具有良好的氧化还原性能和表面酸性。Fe-Mn-CeOx(1:7)/AC@CNTs催化剂在整个温度窗口表现出最高的催化活性，其中，在225～300 ℃范围内，NO转化率达到90%以上，300 ℃时，CB转化率>90%。此外，当CB存在时，300 ℃时，Fe-Mn-CeOx(1:7)/AC@CNTs催化剂的NO转化率依然能达到95%。     

Effect of Carbon Deposits on Reactivity of Supported Pd Model Catalysts

Alumina-supported Pd model catalysts were prepared by Pd evaporation onto a thin alumina film grown on a NiAl(110) substrate. Adsorption and co-adsorption of ethene, CO and hydrogen on Pd/Al₂O₃/NiAl(110) covered by carbon species, formed by ethene dehydrogenation at 550 K, was studied by temperature programmed desorption (TPD). TPD results show that carbon deposits do not prevent adsorption but inhibit dehydrogenation of di- bonded ethene. Carbon species suppress CO adsorption in the highly coordinated sites and also suppress the formation of hydrogen ad-atoms on the surface. The ethene hydrogenation reaction performed by co-adsorption of hydrogen and ethene is inhibited by the presence of carbon deposits. The inhibition is independent of particle size studied (1-3 nm). The effects are rationalized in terms of a site-blocking behavior of carbon species occupying highly coordinated sites on the Pd surface.     

Tunability of Propane Conversion over Alumina Supported Pt and Rh Catalysts

Propane conversion over alumina supported Pt and Rh (1 wt% metals loading) was examined under fuel rich conditions (C₃H₈:O₂:He = 1:2.25:9) over the temperature range 450–650 °C. Morphological characteristics of the catalyst materials were varied by calcining at selected temperatures between 500 and 1,200 °C. X-ray diffraction and BET analysis showed the treatment generated catalyts metals with particle sizes in the range of <10 to >500 nm, and support surface areas in the range of 20–240 m²/g. Remarkably, both Rh and Pt yielded product compositions close to equilibrium values (with high H₂ and CO selectivity, complete oxygen conversion and almost complete propane conversion) so long as the metal particle size was sufficiently low, ≲10–15 nm. In cases where the particle size was large, primarily complete oxidation rather than partial oxidation products were observed, along with unreacted C₃H₈, indicative of a direct oxidation pathway in which gas-phase CO and H₂ are not present as intermediate species. It is proposed that the high resistance of Rh to coarsening is largely responsible for the observation of a higher selectivity of this material for syngas products when prepared by procedures similar to those for Pt. Overall, the tunability of the product composition obtained over Rh and Pt via processing steps has direct significance for the incorporation of such catalyts into the anodes of solid oxide fuel cells.     

负载型TiO2催化苯酚和草酸二甲酯酯交换反应

使用负载型TiO2/SiO2催化苯酚和草酸二甲酯酯交换反应合成草酸二苯酯.通过对TiO2/SiO2催化剂进行XRD、BET化学吸附、NH3-TPD、XPS等表征以及活性测试,结果表明在苯酚和草酸二甲酯酯交换反应中,负载型TiO2的催化性能与TiO2在载体表面的分散状态和催化剂的弱酸性密切相关.微晶态TiO2的产生会导致催化性能的下降.确定了较佳的焙烧温度为550℃,以该温度焙烧的TiO2/SiO2为催化剂,TiO2负载量为13%时,草酸二甲酯的转化率、甲基苯基草酸酯与草酸二苯酯的收率分别为53.1%、38.3%、14.5%.初步探讨了该反应条件下催化剂的失活.     

Catalytic Activity of Supported Platinum and Metal Oxide Catalysts for Toluene Oxidation

Oxidation of toluene has been investigated over supported platinum as well as over a variety metal oxide (M _x O _y ) catalysts dispersed on high surface area γ-Al₂O₃. Catalysts were characterized with respect to their specific surface area (BET), metal dispersion (selective chemisorption of CO), phase composition and M _x O _y crystallite size (XRD) and reducibility (H₂-TPR). Catalytic performance for the title reaction was investigated in the temperature range of 100–500 °C, using a feed composition consisting of 0.1% toluene in air. For Pt/M _x O _y catalysts, it has been found that catalytic performance depends on the nature of the support, with Pt/CeO₂ being the most active catalyst at low temperatures. The intrinsic reaction rate per surface platinum atom does not depend on Pt loading (0.5–5 wt%), at least for Pt/Al₂O₃. Reducible metal oxides, such as ceria, are active for the title reaction and catalytic performance is improved significantly with increase of specific surface area (SSA). However, the intrinsic reaction rate per unit surface area is invariant with SSA. Dispersion of M _x O _y on high surface area inert supports, such as Al₂O₃, results in materials with relatively high catalytic activity, which seems to correlate well with the reducibility of metal oxides. Catalytic performance of M _x O _y /Al₂O₃ catalysts can be optimized by proper selection of M _x O _y loading. Best performing catalysts of this series include 60% MnO, 90% CeO₂ and 5% CuO on Al₂O₃ which, under the present experimental conditions, are able to completely convert toluene toward CO₂ at temperatures lower than 350 °C. Dispersion of Pt on M _x O _y /Al₂O₃ catalysts improves significantly the catalytic performance of irreducible M _x O _y but does not alter appreciably the activity of reducible M _x O _y /Al₂O₃ catalysts.     

Pd Nanoparticles and Thin Films for Room Temperature Hydrogen Sensor

We report the application of palladium nanoparticles and thin films for hydrogen sensor. Electrochemically grown palladium particles with spherical shapes deposited on Si substrate and sputter deposited Pd thin films were used to detect hydrogen at room temperature. Grain size dependence of H₂ sensing behavior has been discussed for both types of Pd films. The electrochemically grown Pd nanoparticles were observed to show better hydrogen sensing response than the sputtered palladium thin films. The demonstration of size dependent room temperature H₂ sensing paves the ways to fabricate the room temperature metallic and metal–metal oxide semiconductor sensor by tuning the size of metal catalyst in mixed systems. H₂ sensing by the Pd nanostructures is attributed to the chemical and electronic sensitization mechanisms.     

Direct Decomposition of NO Over Alkaline Earth Metal Oxide Catalysts Supported on Cobalt Oxide

Spinel powders with addition of ZnO into Ga₂O₃–Al₂O₃ were synthesized from a mixed solution of nitrate salts in the presence of aqueous ammonium carbonate under hydrothermal conditions at 150 °C for 48 h. The crystallization of the spinel was promoted by an increase in reaction temperature and time. This powder was studied for the selective reduction of NO with hydrocarbons (CH₄, C₂H₄, and C₃H₆) in the presence of oxygen. High durability was observed for the reduction of NO by C₂H₄ in the presence of water vapor and sulfur oxides, maintaining a high stability over 100 h.