Controlled deactivation of a skeletal nickel catalyst with sodium silfide in liquid-phase hydrogenation reactions

The kinetics of the liquid-phase hydrogenation of sodium maleate on skeletal nickel catalysts subjected to controlled deactivation with sodium sulfide solutions was studied. The possibility of reactivating partially deactivated skeletal nickel was systematically studied for the first time, and it was found that its activity in liquid-phase hydrogenation reactions can be regulated by the introduction of a catalyst poison in small amounts into the system.     

利用乙醇重整制氢进行硝基苯原位液相加氢合成苯胺

 利用乙醇液相催化重整制得的氢直接进行硝基苯原位液相加氢合成苯胺. 考察了不同催化剂、反应温度及反应时间等因素的影响. 在以Pt/Al2O3为催化剂,反应温度220 ℃和反应时间3 h的条件下,硝基苯的转化率可达99.3%, 苯胺的选择性为99.8%, 催化剂表现出较高的加氢活性和选择性.     

The Effect of Chemical Reducing Agents in the Synthesis of Sol-Gel Ru-Sn Catalysts: Selective Hydrogenation of Cinnamaldehyde

The influence of chemical reduction on the properties of bimetallic Ru-Sn/SiO₂ catalyst was studied. Prepared sol-gel catalysts were reduced by NaBH₄, KBH₄, H₂, and CH₂O. Physical and catalytic properties of reduced catalysts were compared to non-reduced ones in the liquid-phase hydrogenation of cinnamaldehyde. The influence of boron impregnation was investigated. The observed hydrogenation activity and selectivity towards cinnamylalcohol were effected by reduction pretreatment. The NaBH₄ reduced catalyst exhibited the highest activity and selectivity. Reduction pretreatment influenced the pore sizes, active metal surface as well as content of carbon impurities. Traces of the reduction agents were detected in the catalysts. Boron impregnation presumably improved the catalyst activity, but had a minor effect on the selectivity.     

Kinetics of the Hydrogenation of Pinane Hydroperoxide to Pinanol on Pd/C

The liquid-phase hydrogenation of pinane hydroperoxide (PHP) to pinanol on a Pd/C catalyst at 20–80°C and hydrogen pressures of 1–11 atm was studied. It was found that the rate of hydrogenation decreased with PHP concentration. The rate of PHP hydrogenation dramatically increased as the pressure of hydrogen was increased in a range of 2.5–3 atm. A mechanism was proposed for the hydrogenation of PHP. According to this mechanism, the step of hydrogen activation (homolytic or heterolytic addition) depends on the redox properties of the catalyst surface (the ratio between adsorbed PHP species and H₂). It was found that pinanol can be prepared with high selectivity by the hydrogenation of PHP on a Pd/C catalyst under mild conditions.     

Catalytic activity of the VIII Group metals in the hydrogenation and isomerization of α- and β-pinenes

The kinetic regularities of the liquid-phase hydrogenation and isomerization of α- and β-pinenes over the Pd/C, Ru/C, Rh/C, Pt/C, and Ir/C catalysts were studied at temperatures ranging from 20 to 100 °C and at hydrogen pressures of 1–11 bar using n-octane as the solvent. The hydrogenation and isomerization of α- and β-pinenes occur simultaneously on the Ru/C, Rh/C, Pt/C, and Ir/C catalysts, and the reaction mixture contains the products of double bond hydrogenation, viz., cis- and trans-pinanes. The Ru, Rh, and Pd metals have a higher catalytic activity in β-pinene isomerization than Ir and Pt. Among the VIII Group metals studied, the Pd-based catalyst has the highest catalytic activity in double bond isomerization of α- and β-pinenes. The general scheme of the mechanism of hydrogenation and isomerization of α- and β-pinenes on the Pd/C catalyst was proposed.     

Preparation of silica-supported polysulfoalumoxane–platinum complexes and their catalytic activity in the hydrogenation of aromatics

A novel inorganic polymer, silica-supported polysulfoalumoxane, has been prepared and used as a support for preparing a silica-supported polysulfoalumoxane–platinum complex. It has been used as a catalyst for the hydrogenation of aromatics under mild conditions. The effects of several reaction parameters such as metal loading, temperature and solvents on the hydrogenation of methyl benzoate have been studied. The catalyst showed high activity and selectivity.     

Saturation kinetics and relative reactivity of the double bonds of alicyclic dienes in their hydrogenation

The kinetics of the liquid-phase hydrogenation of cyclodienes with various structures (endo-tricyclo[ 5.2.1.0^2,6]decadiene-3,8 and cis,cis-1,5-cyclooctadiene) by hydrogen over a finely dispersed 1%Pd/C catalyst at atmospheric pressure has been studied. The catalyst provides the possibility for successive saturation of the double bonds of the dienes. The reactivities of the cyclodienes determined by their electron-donating properties have been compared. The solvent nature is the determining factor in the ratio of hydrogen absorption rates in the case of successive saturation of the double bonds of the hydrocarbons. The hydrogenation kinetics of cyclic dienes, including dicyclopentadiene, can be modeled using the Langmuir–Hinshelwood equation when the process is carried out in a perfectly mixed flow reactor.     

Palladium hydrogenation catalyst based on a porous carbon material obtained upon the dehydrochlorination of a chloro polymer

The applicability of a porous carbon material obtained as a result of the “chemical” dehydrochlorination of chlorinated polyvinyl chloride as a support for palladium hydrogenation catalysts was demonstrated. The efficiency of the catalyst was evaluated in the liquid-phase reactions of nitrobenzene hydrogenation and chlorobenzene hydrodechlorination. Although the specific activity of the catalyst was lower by a factor of 3–4 than that of the samples based on Sibunit and carbon nanotubes, the complete conversion of the initial compounds with the selective formation of end products under mild conditions was achieved at a relatively low palladium content (1.5%).     

Selective hydrogenation and Suzuki cross‐coupling reactions of various organic substrates using a reusable polymer‐anchored palladium(II) Schiff base complex

A new polymer‐anchored Pd(II) Schiff base complex has been prepared and characterized using scanning electron microscopy, elemental analysis, atomic absorption spectroscopy, TGA and spectrometric methods such as diffuse reflectance spectra of solid and FT‐IR spectroscopy. This polymer‐anchored palladium catalyst shows excellent catalytic activity in the liquid‐phase hydrogenation reaction of styrene oxide to obtain selectively 2‐phenylethanol at normal pressure of hydrogen gas (1 atm.) at room temperature in DMF medium. We have also studied the liquid‐phase hydrogenation reaction of various organic substrates. The catalyst exhibits excellent catalytic activity for the Suzuki cross‐coupling of various substituted and non‐substituted aryl halides. The influences of various parameters were investigated to optimize reaction conditions. The reusability experiments show that the catalyst can be used five times without much loss in catalytic activity. Copyright © 2012 John Wiley & Sons, Ltd.     

NMR imaging of the distribution of the liquid phase in a catalyst pellet during alpha-methylstyrene evaporation accompanied by its vapor-phase hydrogenation

This communication reports the first application of NMR imaging to study the progress of a multiphase heterogeneous catalytic reaction in situ. Various stationary regimes of alpha-methylstyrene (AMS) hydrogenation on a single Pt/gamma-Al2O3 catalyst pellet have been investigated. The two-dimensional maps of the liquid-phase distribution within the pellet have been obtained in the course of the catalytic reaction, with the pellet temperature rising up to 185 degrees C. The large liquid-phase concentration gradients have been shown to exist under conditions of liquid AMS evaporation accompanied by its vapor-phase hydrogenation. It has been demonstrated that despite a substantial broadening of the NMR lines of liquids permeating porous solids the quantification of the relative amounts of AMS and the major reaction product cumene with spatial resolution across the pellet is feasible.     

Synthesis and characterization of Sibunit-supported Pd–Ga,Pd–Zn,and Pd–Ag catalysts for liquid-phase acetylene hydrogenation

Pd/Sibunit and Pd–M/Sibunit (M = Ga, Zn, or Ag) catalysts have been synthesized, and their catalytic properties in liquid-phase acetylene hydrogenation have been investigated. Doping of the palladium catalyst with a metal M leads to the formation of the Pd₂Ga, PdZn, or Pd_0.46Ag_0.54 bimetallic compound. The bimetallic particles are much smaller (1.6–2.0 nm) than the monometallic palladium particles (4.0 nm). Doping with zinc raises the ethylene selectivity by 25% without affecting the activity of the catalyst. Specific features of the effect of each of the dopants on palladium are reported.     

Ruthenium-tin sol-gel catalysts: effect of the preparation and tin precursor influence

The influence of the synthesis route and the chemical nature of tin precursors on the catalytic properties of supported sol-gel Ru-Sn/SiO₂ catalysts were studied. It was demonstrated that introduction of tin afforded better selectivities than a monometallic sol-gel catalyst in the liquid-phase hydrogenation of cinnamaldehyde; however, the chemical nature of the tin precursor did not influence the catalyst performance. Sol-gel catalyst properties depended significantly upon the preparation method used and on the activation temperature. The selectivity to unsaturated alcohol increased with conversion, which is indicative of the in-situ creation of active sites selective in the carbonyl bond hydrogenation.     

Effect of pretreatment of graphite oxide on activity of platinum supported catalysts in liquid-phase hydrogenation

The effect of the reduction procedure of graphite oxide (GO) on activity of platinum supported catalysts in liquid-phase hydrogenation of nitrobenzene and dec-1-ene was studied. The following methods were applied to prepare the catalysts: simultaneous reduction of graphite oxide and H₂PtCl₆; deposition of platinum on graphite oxide which was preliminary subjected to reduction with sodium tetrahydroborate or hydrazine hydrate, or to thermal reduction at 1000 and 1050 °С. It was shown that at equal Pt particles size of ca. 2 nm the catalyst supported on thermally reduced graphite oxide is more active in the model reactions than the catalysts supported on chemically reduced graphite oxide. The catalyst prepared by simultaneous reduction was the least active.     

High-Selective Catalyst Based on Intermetallic Rh1In1 Particles for Nitrobenzene Hydrogenation

Kinetics and Catalysis - The catalytic performance of a bimetallic RhIn/SiO2 catalyst was studied in the liquid-phase hydrogenation of nitrobenzene. The formation of intermetallic Rh1In1...     

Synthesis and characterization of RuO<Subscript>2</Subscript>@ZrO<Subscript>2</Subscript> core–shell nano particles as heterogeneous catalyst for oxidation of benzylic alcohols in different conditions

In this study, new RuO₂@ZrO₂ core–shell nanoparticles have been produced using simple procedure and characterized by the spectroscopic methods (XRD and HR-TEM techniques). Catalytic activity of the synthesized nano powders has been investigated in the liquid-phase selective oxidation of benzyl alcohols. Also, the effect of some parameters such as optimum weight ratio for Ru doping, catalyst, oxidant type and various solvents was studied in room temperature, reflux, ultrasound, microwave conditions and UV–vis irradiation. The catalyst exhibits excellent activity and high conversion under mild conditions. Furthermore, this reagent was recycled and reused three times in the model reaction.     

High-Density and Thermally Stable Palladium Single-Atom Catalysts for Chemoselective Hydrogenations

Single-atom catalysts (SACs) have shown superior activity and/or selectivity for many energy- and environment-related reactions, but their stability at high site density and under reducing atmosphere remains unresolved. Herein, we elucidate the intrinsic driving force of a Pd single atom with high site density (up to 5 wt %) under reducing atmosphere, and its unique catalytic performance for hydrogenation reactions. In situ experiments and calculations reveal that Pd atoms tend to migrate into the surface vacancy-enriched MoC surface during the carburization process by transferring oxide crystals to carbide crystals, leading to the surface enrichment of atomic Pd instead of formation of particles. The Pd₁/α-MoC catalyst exhibits high activity and excellent selectivity for liquid-phase hydrogenation of substituted nitroaromatics (>99 %) and gas-phase hydrogenation of CO₂ to CO (>98 %). The Pd₁/α-MoC catalyst could endure up to 400 °C without any observable aggregation of single atoms.     

Hydrogenation of p-Chloronitrobenzene on Nanosized Modified NiMoB Catalysts

NiMoB alloy catalyst has been reported to be a good catalyst for the hydrogenation of p-chloronitrobenzene to p-chloroaniline. The objective of this study was to investigate the effect of additives (Pd, La, Fe and Co) on the catalytic properties of NiMoB in the hydrogenation of p-chloronitrobenzene. The catalysts were prepared by chemical reduction method using sodium borohydride as the reducing agent. The molar ratios of Ni/Mo/B/additives in the starting materials were 0.4/1/3/0.1. The catalysts were characterized by inductively coupled plasma-mass spectrometry, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalysts were tested for liquid-phase hydrogenation of p-chloronitrobenzene at 1.2?MPa H₂ pressure and 333–353?K. Adding additives decreased the particle size of modified-NiMoB catalyst, suppressed the growth of the crystalline structure of NiMoB and helped the NiMoB nanocluster maintain its amorphous state. The reaction activity is in the order of the following: Pd-NiMoB?>?La-NiMoB?>?Co-NiMoB?>?NiMoB?>?Fe-NiMoB. Pd itself is the active metal for hydrogenation, but NiPd bimetallic alloy was too active resulting in low selectivity of chloroaniline. The other additives were in the form of hydroxide and acted as a spacer to prevent NiMoB catalysts from sintering and aggregation.     

Catalytic hydrodechlorination on palladium-containing catalysts

The catalytic liquid-phase hydrodechlorination of chlorobenzene on supported palladium-containing catalysts has been investigated. The following processes capable of deactivating the catalyst occur during the liquid-phase hydrodechlorination: the coarsening of supported metal particles, the washoff of the active component with the reaction medium, and potassium chloride deposition on the catalyst surface. The effects of the active component composition and of the preparation method on the hydrodechlorination activity and deactivation stability of the catalysts have been studied. The catalysts have been characterized by several physical methods.     

钯系催化剂的制备及其在催化氢化中的应用

钯系催化剂的制备及其在催化氢化中的应用陈一飞，丘礼元，李和兴（上海师范大学化学系上海２００２３４）关键词钯络合催化剂，镍一钯复合催化剂，催化氢化脂肪烯烃和芳烃硝基衍生物种类繁多，其氢化产物广泛应用在食品工业、染料工业、高分子工业以及日用化工等领域。合...     

Effect of the reduction conditions of the supported palladium precursor on the activity of Pd/C catalysts in hydrogenation of sodium 2,4,6-trinitrobenzoate

The study addresses the effect of the reduction conditions of palladium polynuclear hydroxo complexes (PHC) supported on the Sibunit carbon material on the dispersion of the metal particles and the activity of 0.5%Pd/Sibunit catalysts in the selective hydrogenation of sodium 2,4,6-trinitrobenzoate to 1,3,5-triaminobenzene in an aqueous solution (temperature of 323 or 343 K, pressure of 0.5 MPa). The palladium PHC were reduced using the most common methods pertaining to catalyst preparation: liquid-phase reduction with sodium formate and reduction in a hydrogen flow at elevated temperature. It was found that high-temperature reduction in the gas phase gives rise to Pd particles with a markedly lower dispersion compared with the sample obtained under mild liquid-phase reduction conditions. The catalytic activity of the sample containing large Pd particles proved to be higher than the activity of the catalyst obtained by reduction with sodium formate.