Development of RuO<Subscript>2</Subscript>/Rutile-TiO<Subscript>2</Subscript> Catalyst for Industrial HCl Oxidation Process

Sumitomo Chemical has developed a low energy consuming and green process for the catalytic oxidation of HCl to Cl₂, especially when compared with the electrolysis process. The RuO₂/rutile-TiO₂ catalyst has high catalytic activity and thermal stability due to ultra-fine RuO₂ crystallites that cover the surface of the TiO₂ primary particles with strong interaction. In addition, the silica modified RuO₂/rutile-TiO₂ catalyst shows higher thermal stability by preventing the RuO₂ sintering due to using dispersed SiO₂ particles. With these catalysts, high reaction rates required for industrial applications are achieved, even at low temperatures.     

Study on chemisorption of H<Subscript>2</Subscript>, O<Subscript>2</Subscript>, CO and C<Subscript>2</Subscript>H<Subscript>4</Subscript>on Pt-Ag/SiO<Subscript>2</Subscript>catalysts by microcalorimetry and FTIR

Adsorption microcalorimetry has been employed to study the interaction of ethylene with the reduced and oxidized Pt-Ag/SiO₂catalysts with different Ag contents to elucidate the modified effect of Ag towards the hydrocarbon processing on platinum catalysts. In addition, microcalorimetric adsorption of H₂, O₂, CO and FTIR of CO adsorption were conducted to investigate the influence of Ag on the surface structure of Pt catalyst. It is found from the microcalorimetric results of H₂and O₂adsorption that the addition of Ag to Pt/SiO₂leads to the enrichment of Ag on the catalyst surface which decreases the size of Pt surface ensembles of Pt-Ag/SiO₂catalysts. The microcalorimetry and FTIR of CO adsorption indicates that there still exist sites for linear and bridged CO adsorption on the surface of platinum catalysts simultaneously although Ag was incorporated into Pt/SiO₂. The ethylene microcalorimetric results show that the decrease of ensemble size of Pt surface sites suppresses the formation of dissociative species (ethylidyne) upon the chemisorption of C₂H₄on Pt-Ag/SiO₂. The differential heat vs. uptake plots for C₂H₄adsorption on the oxygen-preadsorbed Pt/SiO₂and Pt-Ag/SiO₂catalysts suggest that the incorporation of Ag to Pt/SiO₂could decrease the ability for the oxidation of C₂H₄.     

Bimetallic Pt<Subscript>0.5</Subscript>Co<Subscript>0.5</Subscript>/SiO<Subscript>2</Subscript> Catalyst: Preparation,Structure, and Properties in Preferential Oxidation of Carbon Monoxide

The Pt_0.5Со_0.5/SiO₂ catalyst has been prepared by the decomposition of a [Pt(NH₃)₄][Co(C₂O₄)₂(H₂O)₂]. 2H₂O binary complex salt supported in the pores of SiO₂ pellets. It has been shown by a complex of physical and chemical methods that Pt_0.5Со_0.5/SiO₂ contains alloy nanoparticles with an average composition Pt0.5Co0.5. The catalytic properties of Pt_0.5Со_0.5/SiO₂ are studied in the preferential oxidation of СО in the reaction mixtures with various compositions. It was found that Pt_0.5Со_0.5/SiO₂ has a high selectivity and makes it possible to decrease the outlet concentration of CO to a level of <10 ppm, and the presence of СО₂ and/or Н₂О in the reaction mixture almost does not affect its catalytic properties. The structure of the catalyst is stable under the conditions of preferential CO oxidation.     

Gold catalysts supported on ZnO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for low-temperature CO oxidation

Gold catalysts with loadings ranging from 0.5 to 7.0 wt% on a ZnO/Al₂O₃ support were prepared by the deposition–precipitation method (Au/ZnO/Al₂O₃) with ammonium bicarbonate as the precipitation agent and were evaluated for performance in CO oxidation. These catalysts were characterized by inductively coupled plasma-atom emission spectrometry, temperature programmed reduction, and scanning transmission electron microscopy. The catalytic activity for CO oxidation was measured using a flow reactor under atmospheric pressure. Catalytic activity was found to be strongly dependent on the reduction property of oxygen adsorbed on the gold surface, which related to gold particle size. Higher catalytic activity was found when the gold particles had an average diameter of 3–5 nm; in this range, gold catalysts were more active than the Pt/ZnO/Al₂O₃ catalyst in CO oxidation. Au/ZnO/Al₂O₃ catalyst with small amount of ZnO is more active than Au/Al₂O₃ catalyst due to higher dispersion of gold particles.     

Selective Amplification of CO Bond Hydrogenation on Pt/TiO2: Catalytic Reaction and Sum‐Frequency Generation Vibrational Spectroscopy Studies of Crotonaldehyde Hydrogenation

The hydrogenation of crotonaldehyde in the presence of supported platinum nanoparticles was used to determine how the interaction between the metal particles and their support can control catalytic performance. Using gas‐phase catalytic reaction studies and in situ sum‐frequency generation vibrational spectroscopy (SFG) to study Pt/TiO₂ and Pt/SiO₂ catalysts, a unique reaction pathway was identified for Pt/TiO₂, which selectively produces alcohol products. The catalytic and spectroscopic data obtained for the Pt/SiO₂ catalyst shows that SiO₂ has no active role in this reaction. SFG spectra obtained for the Pt/TiO₂ catalyst indicate the presence of a crotyl‐oxy surface intermediate. By adsorption through the aldehyde oxygen atom to an O‐vacancy site on the TiO₂ surface, the C?O bond of crotonaldehyde is activated, by charge transfer, for hydrogenation. This intermediate reacts with spillover H provided by the Pt to produce crotyl alcohol.     

Effect of Pt nanoparticle size on the specific catalytic activity of Pt/SiO<Subscript>2</Subscript> and Pt/TiO<Subscript>2</Subscript> in the total oxidation of methane and <Emphasis Type="Italic">n</Emphasis>-butane

The dependence of the specific catalytic activity (A _sp ) of the catalysts Pt/SiO₂ and Pt/TiO₂ in the total oxidation of CH₄ and n-C₄H₁₀ on the Pt nanoparticle size (in the range from 1 to 4 nm) was studied. The specific catalytic activity increases with an increase in the platinum nanoparticle size, indicating that the total oxidation is a structure-sensitive reaction. The structure sensitivity depends on the size of an oxidized molecule: it increases sharply on going from CH₄ to n-C₄H₁₀. The support also exerts a considerable effect on the A _sp value: in the oxidation of both CH₄ and C₄H₁₀ the specific catalytic activity for the catalysts Pt/TiO₂ is 3–4 times that for Pt/SiO₂.     

The influence of plasma chemical treatment of a platinum catalyst on its activity in the dehydrogenation of cyclohexane

The influence of plasma chemical treatments on the catalytic activity of 0.64 wt % Pt/SiO₂ and 1.0 wt % Pt/SiO₂ platinum catalysts in the dehydrogenation of cyclohexane was studied. The state of the surface of the catalysts was examined using X-ray photoelectron spectroscopy. Temperature hysteresis caused by the formation of active carbon was observed in flow experiments. It was shown that the reaction on the initial catalysts occurred on neutral and positively charged Pt particles, and that the active centers contained carbon. After catalyst treatment with a high-frequency plasma in H₂, its activity increased by many times because of the formation of a large number of low-activity centers on positively charged platinum particles also containing carbon. Glow discharge plasma in Ar sharply decreased catalytic activity, and the reaction then predominantly occurred on centers localized on neutral Pt particles, whereas centers on positive Pt particles were blocked. The state of the substrate (silica gel) did not change under the action of plasmas of both kinds.     

X-ray photoelectron study of the interaction of H<Subscript>2</Subscript> and H<Subscript>2</Subscript>+O<Subscript>2</Subscript> mixtures on the Pt/MoO<Subscript>3</Subscript> model catalyst

The effects of H₂ and H₂ + O₂ gas mixtures of varying composition on the state of the surface of the Pt/MoO₃ model catalyst prepared by vacuum deposition of platinum on oxidized molybdenum foil were investigated by X-ray photoelectron spectroscopy (XPS) at room temperature and a pressure of 5–150 Torr. For samples with a large Pt/Mo ratio, the XP spectrum of large platinum particles showed that the effect of hydrogen-containing mixtures on the catalyst was accompanied by the reduction of molybdenum oxide. This effect results from the activation of molecular hydrogen due to the dissociation on platinum particles and subsequent spill-over of hydrogen atoms on the support. The effect was not observed at low platinum contents in the model catalyst (i.e., for small Pt particles). It is assumed for the catalyst that the loss of its hydrogen-activating ability is a consequence of the formation of platinum hydride. Possible participation of platinum hydride as intermediate in hydrogen oxidation to H₂O₂ is discussed.     

Heterogenous catalysis in fine chemistry: the Heck reaction on Pd/SiO<Subscript>2</Subscript> catalysts

The preparation conditions to obtain a Pd/SiO₂ catalyst effective in the Heck reaction between para-substituted halogenobenzene and alkylacrylate have been studied. The impregnation of SiO₂, functionalised with a thiourea derivative, with a Pd(CH₃COO)₂ solution resulted in an active, but unstable catalyst. The catalyst became stable after calcination, but its activity appeared to be strongly dependent on the calcination temperature. IR spectra of adsorbed CO indicated that such a dependence should result from differences in the surface structure of the supported particles.     

Cooperative Effect of Platinum and Alumina on Catalyst Deactivation for Dehydrogenation Reaction

The cooperative effect on catalyst deactivation of Pt-based catalysts for dehydrogenation reaction was investigated using the combination of Pt-based/SiO₂ and Al₂O₃. The presence of the effect was confirmed by reaction test, CO adsorption, H₂-TPD and TPO. Considering conversion, active site, H₂ uptake and the nature and amount of coke, interestingly, the physical mixture of Pt-based catalyst supported on SiO₂ with 100-120 mesh and Al₂O₃ 60-80 mesh was similar to Pt-based Al₂O₃. The concept of combination of two catalytic functions, acidity and metallic species, will certainly provide the possibility of better catalyst design.     

Effect of the microstructure of the supported catalysts CuO/TiO<Subscript>2</Subscript> and CuO/(CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>) on their catalytic properties in carbon monoxide oxidation

The effect of the microstructure of titanium dioxide on the structure, thermal stability, and catalytic properties of supported CuO/TiO₂ and CuO/(CeO₂-TiO₂) catalysts in CO oxidation was studied. The formation of a nanocrystalline structure was found in the CuO/TiO₂ catalysts calcined at 500°C. This nanocrystalline structure consisted of aggregated fine anatase particles about 10 nm in size and interblock boundaries between them, in which Cu²⁺ ions were stabilized. Heat treatment of this catalyst at 700°C led to a change in its microstructure with the formation of fine CuO particles 2.5–3 nm in size, which were strongly bound to the surface of TiO₂ (anatase) with a regular well-ordered crystal structure. In the CuO/(CeO₂-TiO₂) catalysts, the nanocrystalline structure of anatase was thermally more stable than in the CuO/TiO₂ catalyst, and it persisted up to 700°C. The study of the catalytic properties of the resulting catalysts showed that the CuO/(CeO₂-TiO₂) catalysts with the nanocrystalline structure of anatase were characterized by the high-est activity in CO oxidation to CO₂.     

Effect of the preparation conditions on the physicochemical and catalytic properties of Ni<Subscript>2</Subscript>P/SiO<Subscript>2</Subscript> catalysts

The effect of the reduction conditions on the physicochemical and catalytic properties of Ni₂P/SiO₂ catalysts was studied. The catalysts were prepared by impregnating silica with a solution of nickel acetate and diammonium hydrogen phosphate followed by drying, calcination, and temperature-programmed reduction. The Ni₂P/SiO₂ catalysts were reduced prior to hydrodeoxygenation (HDO) of methyl palmitate in the catalytic reactor (in situ) at temperatures of 550, 600, and 650 °С for 3 h and at 600 °С for 1 and 6 h. The reduction temperature and reduction time were shown to affect the conversion of methyl palmitate, and the optimal reduction conditions of the Ni₂P/SiO₂ catalysts were found. The Ni₂P/SiO₂ catalyst synthesized according to a widely used preparation method, including steps of passivation and rereduction at 450 °С in addition to the reduction step, is inferior in activity to the samples prepared in situ.     

Catalytic properties of Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in the aqueous-phase reforming of ethylene glycol: Effect of the alumina support

The influence of the alumina support on the catalytic activity of Pt/Al₂O₃ catalysts in aqueous phase reforming of ethylene glycol to hydrogen was studied. The catalysts were prepared by impregnation of γ-, δ-, and α-alumina with H₂PtCl₆. The highest rate of hydrogen production (452 μmol min⁻¹ g⁻¹) obtained with the Pt/α-Al₂O₃ catalyst can be related to the highest extent of dispersion of Pt on α-Al₂O₃. XPS, TEM-EDX and TPR-H₂ measurements showed the absence of chloride-containing surface complexes in the Pt/α-Al₂O₃ catalyst. However, chloride-containing entities were found on the surface of Pt/γ-Al₂O₃ and Pr/δ-Al₂O₃ catalysts. When chloride ions are removed chlorinated Pt species facilitate the sintering of Pt crystallites and in this way affect the extent of Pt dispersion. Moreover, depending upon the particular crystalline form, alumina atoms have different coordination and alumina surfaces contain varying amounts of OH groups of different nature which affect the interaction between Pt and the support.     

Kinetics of α-olefin metathesis on binary and ternary catalytic systems based on MoCl<Subscript>5</Subscript>/SiO<Subscript>2</Subscript>: Determination of the number of active centers and the mechanisms of their formation,deactivation, and reactivation

The kinetics of α-olefin metathesis in the presence of binary (MoCl₅/SiO₂-Me₄Sn) and ternary catalytic systems (MoCl₅/SiO₂-Me₄Sn-ECl₄, E = Si or Ge) was studied. It was found that reactivation in the course of metathesis occurred on the addition of a third component (silicon tetrachloride or germanium tetrachloride in combination with tetramethyltin) to a partially deactivated catalyst. The number of active centers was determined (5–6% of the amount of Mo), and the mechanisms of formation, deactivation, and reactivation were proposed for the binary and ternary catalytic systems. The roles of the individual components of the catalytic systems were revealed.     

SiO2和Al2O3负载的Ni基催化剂在甲烷干重整中的催化性能差异

CH₄与CO₂干重整反应对于环境保护和天然气资源的合理利用具有重要意义。SiO₂和Al₂O₃是适用于甲烷干重整反应的两种典型的催化剂载体。为了阐明这两种载体对催化剂性能的影响,本研究采用等体积浸渍法制备了Ni/Al₂O₃和Ni/SiO₂催化剂,并利用BET、TEM、H₂-TPR、XRD、TG和Raman等技术对还原和反应后的催化剂进行了表征。结果表明,由于载体的性质不同,Ni基催化剂在甲烷干重整中的催化性能也不同。Ni/SiO₂催化剂的初始活性较高,但由于其金属-载体相互作用较弱,催化稳定性较差,在800℃下反应15h其催化活性急剧下降;较弱的金属-载体相互作用使得Ni/SiO₂催化剂上的Ni颗粒较大,有利于积炭前驱物种的生成,导致催化剂快速失活。而对于Ni/Al₂O₃催化剂,金属-载体相互作用较强,Ni颗粒较小,但由于Ni与Al₂O₃生成了NiAl_xO_y物种,有效活性位减少,其催化活性相对较低,但催化稳定性较好,干重整反应进行50h其活性保持稳定;Ni与Al₂O₃之间较强的相互作用有利于形成小且稳定的Ni粒子,能减少积炭,因而具有优异的催化稳定性。     

Dependence of the adsorption and catalytic properties of a copper-platinum catalyst on the structure of metal particles and the composition of the catalyst surface

The kinetics of H₂ desorption from the surface of a copper-platinum catalyst deposited on silica gel ([1 wt % Pt + 0.15 wt % Cu]/SiO₂) and the kinetics of C₆H₁₂ dehydrogenation were studied. The effects of copper introduction in a platinum catalyst on the structural characteristics of platinum particles, the composition of their surface, and the effects of plasmochemical treatments on these parameters were studied by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The metal-H atom bond energies (E _Pt-H) and the catalytic activity were found to increase in the presence of Cu. This was explained by the formation of new hydrogen adsorption centers (due to the Cu^+δ adatoms) and catalytic centers composed of Cu^+δ adatoms and carbon atoms. The mean diameter of Pt particles (D) increased twofold. The microstresses (ɛ) in the particles increased after the catalyst was treated with glow discharge plasma in Ar and O₂ and with high-frequency plasma in H₂ (HF-H₂). The observed changes in the bond energy E _Pt-H and kinetic parameters were explained by the increase in microstresses in Pt particles.     

Study of <Emphasis Type="Italic">n</Emphasis>-hexane isomerization on Pt/SO<Subscript>4</Subscript>/ZrO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts: Effect of the state of platinum on catalytic and adsorption properties

The state of surface Pt atoms in the Pt/SO₄/ZrO₂/Al₂O₃ catalyst and the effect of the state of platinum on its adsorption and catalytic properties in the reaction of n-hexane isomerization were studied. The Pt-X/Al₂O₃ alumina-platinum catalysts modified with various halogens (X = Br, Cl, and F) and their mechanical mixtures with the SO₄/ZrO₂/Al₂O₃ superacid catalyst were used in this study. With the use of IR spectroscopy (CO_ads), oxygen chemisorption, and oxygen-hydrogen titration, it was found that ionic platinum species were present on the reduced form of the catalysts. These species can adsorb to three hydrogen atoms per each surface platinum atom. The specific properties of ionic platinum manifested themselves in the formation of a hydride form of adsorbed hydrogen. It is believed that the catalytic activity and operational stability of the superacid system based on sulfated zirconium dioxide were due to the participation of ionic and metallic platinum in the activation of hydrogen for the reaction of n-hexane isomerization.     

Catalytic efficiency of cesium and potassium salts of dodecatungstophosphoric acid supported on silica and comparison with H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>/SiO<Subscript>2</Subscript>

Pure tungstophosphoric acid, potassium tungstophosphate, and cesium tungstophosphate with varying extent of substitution of protons by Cs or K ions x (x = 1, 2, 2.5, and 3) have been prepared and are supported on silica by the wet impregnation method. The extent of loading was fixed at 20 wt %. For the sake of comparison, unloaded Cs _x and K _x (x = 1) salts of tungstophosphoric acid were prepared by the precipitation method. The supported catalysts were characterized by FT-IR, XRD, specific surface area measurements, and catalytic conversion of tert-butanol. The results revealed that the catalytic conversion of tert-butanol proceeds mainly via dehydration yielding isobutene. The Cs₁PW/SiO₂, HPW/SiO₂, and K₁PW/SiO₂ catalysts were more active than their unsupported samples. The previous solids showed greater catalytic activity and stability. Unexpectedly, substitution of one proton of tungstophosphoric acid by a cesium or potassium ion exerted no measurable effect on the catalytic activity of the treated solids, in spite of decreasing the Brønsted acidity of Cs₁PW/SiO₂ and K₁PW/SiO₂ indicating that the acidity of HPW/SiO₂ decrease may be due to the interaction between HPW and the SiO₂ surface. On the other hand, significant decrease in the catalytic activity took place upon increasing the cation content (x) to x = 2, 2.5, and 3.     

Thermal activation effect on catalytic systems MnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for deep oxidation of hydrocarbons

The effect of thermal activation, sharp increase in the catalytic activity of the system MnO _x -Al₂O₃ in reactions of deep oxidation of CO and hydrocarbons after calcination of the catalyst at 900–1000°C was discovered and investigated. With the use of X-ray phase analysis, X-ray electron spectroscopy, EXAFS, IR spectroscopy, electronic spectroscopy of diffuse reflections, electron microscopy etc. it was established that the effect of thermal activation is related to reversible phase transitions in the system at heating and cooling. On cooling from 1100°C to 650°C disperse particles of cubic spinel of composition Mn_{2.1 ? x} · Al_{0.9 + x} O₄ are conserved on the corundum surface. On further cooling the spinel decomposes and finally the nanocristalline species of β-Mn₃O*₄ containing up to 15 at% of Al³⁺ form and govern the activity.The thermal activation effect was implemented in an industrial catalyst IK-12-40. Joint Stocks Co “KATALIZATOR” produced and supplied to customers hundreds of tons of this catalyst. The catalyst was awarded with a silver medal of the International exhibition EUREKA in Brussels (1995).     

Hollow PtFe Alloy Nanoparticles Derived from Pt-Fe3O4 Dimers through a Silica-Protection Reduction Strategy as Efficient Oxygen Reduction Electrocatalysts

The development of efficient and stable electrocatalysts for the oxygen reduction reaction (ORR) is critical for the large-scale production of fuel cells. Platinum (Pt) nanoparticle catalysts show excellent performance for ORR, though the high cost of Pt is a limiting factor that directly impacts fuel cell production costs. Alloying Pt with other transition metals is an effective strategy to reduce Pt utilization whilst maintaining good ORR performance. In this work, novel hollow PtFe alloy catalysts were successfully synthesized by high-temperature pyrolysis of SiO₂-coated Pt-Fe₃O₄ nanoparticle dimers supported on carbon at 900 °C, followed by SiO₂ shell removal and partial dealloying of the PtFe nanoparticles formed using HF. The obtained hollow PtFe nanoparticle catalysts (denoted herein as PtFe-900) showed a 2.3-fold enhancement in ORR mass activity compared to PtFe nanoparticles synthesized without SiO₂ protection, and a remarkable 7.8-fold enhancement relative to a commercial Pt/C catalyst. Further, after 10 000 potential cycles, the ORR mass activity of PtFe-900 remained very high (90.9 % of the initial mass activity). The outstanding ORR performance of PtFe-900 can be attributed to the modification of Pt lattice and electronic structure by alloying with Fe at high temperature under the protection of the SiO₂ coating. This work guides the development of improved, highly dispersed Pt-based alloy nanoparticle catalysts for ORR and fuel cell applications.