Selective Oxidation of Glucose to Gluconic Acid over Bimetallic Pd–Me Catalysts (Me = Bi,Tl, Sn,Co)

Catalytic properties of bimetallic Pd–Bi, Pd–Tl, Pd–Sn, and Pd–Co catalysts supported on C (from plum stones) and SiO₂ were studied in the reaction of glucose oxidation to gluconic acid. Catalysts modified with Bi show the best selectivity and activity. The results obtained from research on 5% Pd–5% Bi/C and 5% Pd–5% Bi/SiO₂ catalytic systems were compared with the results for a commercial catalyst containing 1% Pt–4% Pd–5% Bi supported on active carbon (Degussa). For both Pd–Bi/support catalysts and 1% Pt–4% Pd–5% Bi/C, similar selectivity in the reaction of glucose oxidation was observed. XRD studies proved the presence of intermetallic compounds BiPd and Bi₂Pd, which probably increase the selectivity of PdBi/SiO₂ catalysts.     

Catalysts and Processes for Paraffin and Olefin Dehydrogenation1

General trends in the development of industrial processes and catalysts for the dehydrogenation of lower C₃–C₅ paraffins and olefins are considered. A brief review of studies on the improvement of commercial nickel–calcium phosphate and iron oxide catalysts for the dehydrogenation of olefins and ethylbenzene to dienes and styrene, respectively, performed in the Laboratory of Dehydrogenation at the Boreskov Institute of Catalysis (Siberian Division, Russian Academy of Sciences) in collaboration with OAO NPO Yarsintez is given. The results of studies on the development of new spinel-supported bimetallic Pt–Sn catalysts for the steam dehydrogenation of lower paraffins are presented.     

Synthesis of carbon-supported sub-2 nanometer bimetallic catalysts by strong metal–sulfur interaction

Small-sized bimetallic nanoparticles that integrate the advantages of efficient exposure of the active metal surface and optimal geometric/electronic effects are of immense interest in the field of catalysis, yet there are few universal strategies for synthesizing such unique structures. Here, we report a novel method to synthesize sub-2 nm bimetallic nanoparticles (Pt–Co, Rh–Co, and Ir–Co) on mesoporous sulfur-doped carbon (S–C) supports. The approach is based on the strong chemical interaction between metals and sulfur atoms that are doped in the carbon matrix, which suppresses the metal aggregation at high temperature and thus ensures the formation of small-sized and well alloyed bimetallic nanoparticles. We also demonstrate the enhanced catalytic performance of the small-sized bimetallic Pt–Co nanoparticle catalysts for the selective hydrogenation of nitroarenes.

The strong interactions between metal and sulfur atoms doped in a carbon matrix allow for the synthesis of supported sub-2 nanometer M–Co (M = Pt, Rh, Ir) bimetallic nanocluster catalysts.     

贵金属助剂对费-托合成用钴基催化剂的促进作用

贵金属助剂促进的费-托合成用钴基催化剂具有高活性和长链烃(C₅⁺)选择性优越等特点,被广泛应用于由合成气制清洁燃料的合成反应中。 本文重点讨论了贵金属助剂对活性钴物种的结构（还原度、分散度、双金属颗粒或合金的构成）, 钴基催化剂稳定性以及其对费-托合成的反应速率和产物选择性的影响规律。     

MIL‐100(Fe) Supported Pt−Co Nanoparticles as Active and Selective Heterogeneous Catalysts for Hydrogenation of 1,3‐Butadiene

Superior catalytic performance for selective 1,3‐butadiene (1,3‐BD) hydrogenation can usually be achieved with supported bimetallic catalysts. In this work, Pt−Co nanoparticles and Pt nanoparticles supported on metal–organic framework MIL‐100(Fe) catalysts (MIL=Materials of Institut Lavoisier, PtCo/MIL‐100(Fe) and Pt/MIL‐100(Fe)) were synthesized via a simple impregnation reduction method, and their catalytic performance was investigated for the hydrogenation of 1,3‐BD. Pt1Co1/MIL‐100(Fe) presented better catalytic performance than Pt/MIL‐100(Fe), with significantly enhanced total butene selectivity. Moreover, the secondary hydrogenation of butenes was effectively inhibited after doping with Co. The Pt1Co1/MIL‐100(Fe) catalyst displayed good stability in the 1,3‐BD hydrogenation reaction. No significant catalyst deactivation was observed during 9 h of hydrogenation, but its catalytic activity gradually reduces for the next 17 h. Carbon deposition on Pt1Co1/MIL‐100(Fe) is the reason for its deactivation in 1,3‐BD hydrogenation reaction. The spent Pt1Co1/MIL‐100(Fe) catalyst could be regenerated at 200 °C, and regenerated catalysts displayed the similar 1,3‐BD conversion and butene selectivity with fresh catalysts. Moreover, the rate‐determining step of this reaction was hydrogen dissociation. The outstanding activity and total butene selectivity of the Pt1Co1/MIL‐100(Fe) catalyst illustrate that Pt−Co bimetallic catalysts are an ideal alternative for replacing mono‐noble‐metal‐based catalysts in selective 1,3‐BD hydrogenation reactions.     

CO hydrogenation over small Pt, Ir and Pt?Ir bimetallic clusters entrapped in the supercage of NaY zeolite

In CO hydrogenation, small (ca. 1 nm) Pt–Ir bimetallic clusters encapsulated in the supercage of NaY zeolite showed significant non-linear Schulz-Flory distributions, especially high selectivity for C₄ hydrocarbons, which is different from those of Pt or Ir clusters entrapped inside the supercage of NaY.     

One-step synthesis of carbon-supported Pd–Pt alloy electrocatalysts for methanol tolerant oxygen reduction

A facile, one-step reduction route was developed to synthesize Pd-rich carbon-supported Pd–Pt alloy electrocatalysts of different Pd/Pt atomic ratios. As-prepared Pd–Pt/C catalysts exhibit a single phase fcc structure and an expansion lattice parameter. Comparison of the oxygen reduction reaction (ORR) on the Pd–Pt/C alloy catalysts indicates that the Pd₃Pt₁/C bimetallic catalyst exhibits the highest ORR activity among all the Pd–Pt alloy catalysts and shows a comparative ORR activity with the commercial Pt/C catalyst. Moreover, all the Pd–Pt alloy catalysts exhibited much higher methanol tolerance during the ORR than the commercial Pt/C catalyst. High methanol tolerance of the Pd–Pt alloy catalysts could be attributed to the weak adsorption of methanol induced by the composition effect, to the presence of Pd atoms and to the formation of Pd-based alloys.     

Highly stable Pt–Ru/C as an anode catalyst for use in polymer electrolyte fuel cells

A new method for preparing highly stable Pt–Ru/C catalysts at low temperature is reported. Pt–Ru supported on high surface carbon was prepared from Pt(NH₃)₄Cl₂, RuNO(NO₃) _x (OH) _y and borohydride as a reducing agent. Simultaneous reduction of both metals was done by heat treatment and small and homogeneously dispersed catalyst particles were obtained with increased stability, as observed from solubility tests. Catalysis, XRD and TG data gave clear evidence of the different chemical states between the material produced and the commercially available sample. The electrochemical measurements showed that the novel catalysts have a performance similar to that of E-Tek samples.     

Cyclohexane transformations over metal oxide catalysts. 2. Selective cyclohexane ring opening to form n-hexane over mono- and bimetallic rhodium catalysts

The activity of monometallic Rh and Pt catalysts and bimetallic Pt—Rh catalysts on oxide supports in cyclohexane ring opening to form n-hexane was studied. The Rh-containing catalysts are highly active and selective in this reaction. Cyclohexane dehydrogenation predominates in the case of the Pt catalysts. The use of the bimetallic alumina-supported Pt—Rh catalysts allows one to minimize the contribution of cyclohexane cracking and to enhance the selectivity for n-hexane with the yield of the latter slightly depending on the metal ratio in the bimetallic system under the experimental conditions.     

Formation of C1–C5 Hydrocarbons from CCl4 in the Presence of Carbon-Supported Palladium Catalysts

Along with hydrodechlorination, the formation of C₁ and higher hydrocarbons takes place in a flow system in the presence of catalysts containing 0.5–5.0% Pd supported on a Sibunit carbon carrier at 150–230°C. In the entire range of conditions examined, the reaction products are primarily methane, C₂–C₄ hydrocarbon fractions, and C₅ traces. The catalysts are stable in operation, and a high conversion of CCl₄ was retained for a long time interval. The nonselective formation of linear and branched hydrocarbons is indicative of a radical mechanism of the process.     

Thallium as an Additive Modifying the Selectivity of Pd/SiO2 Catalysts

Catalytic properties of palladium and bimetallic palladium–thallium catalysts supported on SiO₂ in the reaction of glucose oxidation to gluconic acid were studied. Catalysts modified with thallium showed better selectivity and activity than palladium catalysts. XRD studies proved the presence of intermetallic interactions, which probably increase the selectivity of Pd–Tl/SiO₂ catalysts. Particular attention was paid to the losses of thallium and palladium from the catalysts during the catalytic reaction.     

Effect of substitution of Fe3+ in CuCr2O4 matrix for the hydrogenation of nitrobenzene

The hydrogenation of nitrobenzene to aniline over reduced Cu(Fe_xCr_2–x)O₄ series of catalysts (where x=0, 0.2, 0.4, 0.6, 0.8 and 1.0) has been studied at 250°C in a fixed bed flow type reactor. All the catalysts were characterized by XRD, IR and DRS analysis and by measurements of electrical conductivity and surface area. The conversion of nitrobenzene to aniline is maximum over the catalysts with composition x=0.4. By comparing the results of reversible and irreversible adsorption of carbon monoxide with hydrogenation activity, it can be concluded that univalent copper at octahedral sites is more active for hydrogenation than metallic copper. The second cations [Cr(III) or Fe(III)] develop their catalytic activity by sharing anionic vacancies.     

The Synergistic Effect of a Bimetallic Catalyst for the Synthesis of Carbon Nanotube Aerogels and their Predominant Chirality

Synthesis of continuous spinnable carbon nanotube (CNT) fibers is the most promising method for producing CNT fibers for commercial applications. The floating-catalyst chemical vapor deposition (FC-CVD) method is a rapid process that achieves catalyst formation, CNT nucleation and growth, and aerogel-like sock formation within a few seconds. However, the formation mechanism is unknown. Herein, the progress of CNT fiber formation with bimetallic catalysts was studied, and the effect of catalyst composition to CNT fiber synthesis and their structural properties was investigated. In the case of bimetallic catalysts, the carbon source rapidly decomposes and generates various secondary hydrocarbon species, such as CH₄, C₂H₄, C₂H₂, C₃H₆, and C₄H₁₀ whereas monometallic catalysts generate only CH₄ and C₂H₄ on decomposition. CNT fiber formation with Fe₁Ni₀ begins about 400 mm from the reactor entrance, whereas CNT formation with Fe_0.8Ni_0.2 and Fe_0.5Ni_0.5 begins at about 500 and 300 mm, respectively. The formed CNT bundles and individual CNTs are oriented along the gas flow at these locations. The enhanced rate of fiber formation and lowering of growth temperature associated with bimetallic catalysts is explained by the synergistic effects between the two metals. The synthesized CNTs become predominantly semiconducting with increasing Ni contents.     

Synergism of hydrogenating capacity in the Ni-Pd/Al2O3 system

In liquid-phase hydrogenation of ethyl acetoacetate on bimetallic Ni-Pd catalysts supported on Al₂O₃, the reaction rate increases sharply and passes through a maximum with an increase in the concentration of Pd. The change in the rate of hydrogenation with a change in the composition of the catalysts is not due to a change in the dispersion of the metallic phase in them or enrichment of their surface with one of the metals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 11–13, January, 1990.     

Formation of a supported cobalt catalyst for the synthesis of carbon nanofibers on aluminum oxide

Comparative studies of the effect of the physicochemical characteristics of a support (aluminum oxide) on the formation of a supported Co catalyst and its activity in the pyrolysis of alkanes (propane-butane) were performed. The effect of the crystalline modification of alumina on the yield of catalytic filamentous carbon (CFC) ((g CFC)/(g Co)) was studied. The surface morphologies of Co-containing catalysts and synthesized carbon deposits were studied by scanning electron microscopy. It was found that carbon deposits with a well-defined nanofiber structure were synthesized by the pyrolysis of a propane-butane mixture in the presence of hydrogen at 600°C on supported Co catalysts prepared by homogeneous precipitation on macroporous corundum (α-Al₂O₃). The yield of CFC was no higher than 4 (g CFC)/(g Co). On the Co catalyst prepared by homogeneous precipitation on mesoporous Al₂O₃, the intense carbonization of the initial support; the formation of cobalt aluminates; and, as a consequence, the deactivation of Co⁰ as a catalyst of FC synthesis occurred. The dependence of the yield of CFC on the preheating temperature (from 200 to 800°C) of Co catalysts before pyrolysis was studied. It was found that, as the preheating temperature of supported Co/Al₂O₃ catalysts was increased, the amount of synthesized carbon, including CFC, decreased because of Co⁰ deactivation due to the interaction with the support and coke formation.     

Combustion of methane over supported palladium-copper bimetallic catalysts

Monometallic and bimetallic catalysts based on palladium and copper deposited on a spinel carrier have been investigated in the catalytic combustion of methane. Great differences were found in catalytic activity, according to the sequence Pd/MgAl₂O₄>CuO–Pd/MgAl₂O₄>Pd–CuO/MgAl₂O₄>CuO/MgAl₂O₄. They were explained by changes in surface composition of the catalysts. In the case of bimetallic catalysts the metallic surface is preferentially enriched in copper, which acts as a diluting agent for the Pd atom ensembles. As a consequence, the adsorption of reactants is limited and the catalysts so obtained behave like copper slightly doped with palladium.     

Methane conversion by various metal, metal oxide and metal carbide catalysts

The progress in the field of methane conversion into higher hydrocarbons including aromatics and oxygenated compounds in the recent five years will be reviewed shortly, together with a new type of the methane conversion reaction with carbon monoxide at lower temperatures (600–700 K) by supported group VIII metal catalysts. Benzene was formed selectively among hydrocarbons in the CH₄–CO reaction over silica-supported Rh, Ru, Pd and Os catalysts under atmospheric pressure. Both CH₄ and CO were required for benzene formation, and only ethane and ethylene were formed besides benzene. The amount of C₃–C₅ hydrocarbons was negligible, which suggests that a completely different mechanism from the CO–H₂ reaction may be operating over these catalysts despite of the similarity in the reaction conditions with the CO–H₂ reaction. The mechanism of benzene formation was studied deeply by means of kinetical investigation as well as infrared spectroscopy and isotopic tracer method in connection with that of CO hydrogenation.     

Characteristics of hydrogen and carbon monoxide adsorption on supported rhodium-containing bimetallic catalysts

The methods of temperature-programmed desorption and microcalorimetry were used to determine the kinetic and thermodynamic characteristics of H₂ and CO adsorption on the surface of rhodium in bimetallic catalysts. The relationship between the chemical composition of the catalysts studied, electronic state of Rh, and parameters of the adsorption processes was determined.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 31, No. 2, pp. 114–119, March–April, 1995.     

Selective deposition of Sn on the Pt surface of Pt/ZnAl2O4 catalyst and addition effect on isobutane dehydrogenation

Pt−Sn bimetallic catalysts were prepared by a CVD technique in which Sn was added by passing volatile organometallic compounds over Pt/ZnAl₂O₄ in a H₂ flow. Mixed Pt−Sn sites improve the activity of isobutane dehydrogenation, while Sn on the support improves the selectivity.     

Pt–Fe cathode catalysts to improve the oxygen reduction reaction and methanol tolerance in direct methanol fuel cells

High surface area carbon-supported Pt and bimetallic Pt–Fe catalysts are investigated for the oxygen electro-reduction reaction (ORR) in low-temperature direct methanol fuel cells (60 °C). The electrocatalysts are prepared using a combination of colloidal and incipient wetness methods allowing the synthesis of carbon-supported bimetallic nanoparticles with a particle size of about 2–3 nm. These materials are studied in terms of structure, morphology and composition using X-ray diffraction, X-ray fluorescence and transmission electron microscopy techniques. The electrocatalytic behaviour of these catalysts for ORR is investigated by employing the rotating disc technique. An enhancement of the ORR is observed with the bimetallic Pt–Fe catalyst in the oxygen-saturated electrolyte solution, with and without methanol. Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to interfacial electrochemistry.