Catalytic Activity Of Bimetallic Catalysts Research Articles

High-Throughput Screening of Sulfur-Resistant Catalysts for Steam Methane Reforming Using Machine Learning and Microkinetic Modeling.

The catalytic activity of bimetallic catalysts for the steam methane reforming (SMR) reaction was extensively studied previously. However, the performance of these materials in the presence of sulfur-containing species is yet to be investigated. In this study, we propose a novel process aided by machine learning (ML) and microkinetic modeling for the rapid screening of sulfur-resistant bimetallic catalysts. First, various ML models were developed to predict atomic adsorption energies (C, H, O, and S) on bimetallic surfaces. Easily accessible physical and chemical properties of the metals and adsorbates were used as input features. The Ensemble learning, artificial neural network, and support vector regression models achieved the best performance with R2 values of 0.74, 0.71, and 0.70, respectively. A microkinetic model was then built based on the elementary steps of the SMR reaction. Finally, the microkinetic model, together with the atomic adsorption energies predicted by the Ensemble model, were used to screen over 500 bimetallic materials. Four Ge-based alloys (Ge3Cu1, Ge3Ni1, Ge3Co1, and Ge3Fe1) and the Ni3Cu1 alloy were identified as promising and cost-effective sulfur-resistant catalysts.

The Application of Copper-Gold Catalysts in the Selective Oxidation of Glycerol at Acid and Basic Conditions

The crude glycerol is produced during the transesterification of animal fats and vegetable oils, but it is a by-product of this process. Currently, its elimination is a problem in the chemical industry. The main goal of this work was the preparation, characterization and application of mesoporous cerium-zirconium oxide as supports for copper and gold species and the comparison of selected factors on the properties of catalysts in glycerol oxidation in the liquid phase. The samples were characterized using adsorption and desorption of nitrogen, XRD, UV-vis, XPS, TEM, SEM, and STEM-EDXS. The obtained results of glycerol oxidation show that the bimetallic copper-gold catalysts are more active and selective to glyceric acid in this reaction than analogous monometallic gold catalysts. Additionally, bimetallic catalysts are also characterized by the catalytic stability, and their application leads to the increase of selectivity to glyceric acid during their reusing in glycerol oxidation in alkali media. In this work, the influence of selected factors, e.g., oxygen source and its pressure, solution pH, and base content on the catalytic activity of bimetallic catalysts is discussed.

Pt-alloy decorated graphene as an efficient electrocatalyst for PEM fuel cell reactions

Herein, for the first time, bimetallic nanoparticles supported on graphene nanoplatelets (PtNi/GNPs, PtFe/GNPs, PtCu/GNPs) were prepared as sequentially through supercritical carbon dioxide (scCO2) technique. The physicochemical properties of the prepared catalysts were characterized by XRD, TEM, EDX, TGA, ICP-MS and Raman spectroscopy. Furthermore, the catalytic activity of bimetallic catalysts was tested using a three-cell cyclic voltammetry. PtNi/GNPs catalyst showed the best catalytic activity towards both hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR). Finally, to investigate the improvement of the cell performances, polarization curves were presented. It was found that the PtNi/GNPs catalyst exhibited highest performance (907.5 mA/cm 2, 0.54 mW/cm 2 @ 0.6 V) when the catalyst was used as anode electrode. We believe that this work will serve as a guide to the fuel cell research community in the selection of a promising route for the development of new low-cost and efficient electrocatalysts for PEMFC.

Oxidation of toluene in humid air by metal oxides supported on γ-alumina

Monometallic and bimetallic supported metal oxides catalysts on γ-alumina were prepared by heterogeneous deposition-precipitation. The γ-alumina used as a support was synthesized by the sol-gel and the co-precipitation methods. Supports and catalysts were characterized by Brunauer–Emmett–Teller (BET) surface area, X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The performance of the prepared catalysts was studied for total oxidation of toluene in air at different relative humidity and oxidation temperatures. Efficiency of bimetallic catalysts for deep oxidation of toluene was higher than copper oxide supported on γ-alumina. Although increasing the lanthanum, cobalt, and nickel loading on the support led to a modified catalyst surface and morphology, the catalytic activity of bimetallic catalysts decreased with increasing lanthanum, cobalt, and nickel content due to the reduced amount of copper oxide which has a higher activity for oxidation of volatile organic compounds. The γ-alumina prepared by the sol-gel method using ethanol as a solvent (AlSE) was the best support and La-Cu/AlSE had the best performance (toluene removal efficiency >90%). In addition, the presence of water vapor in the feed had a negative effect on toluene conversion.

Synergetic effect of Pd addition on catalytic behavior of monolithic platinum–manganese–alumina catalysts for diesel vehicle emission control

The advanced diesel emission control catalyst Pt–Pd–MnOx–Al2O3 has been developed on the basis of the synergetic effect of Pt with Pd and manganese oxides observed in hydrocarbon and carbon monoxide oxidation reactions. This effect allows a decrease in the total loadings of Pt and Pd down to 0.52g/L in the monolithic catalyst, providing high activity in low temperature oxidation of light hydrocarbons and high thermal stability.The catalytic activity of Pt–Pd–MnOx–Al2O3 monolithic catalysts in butane oxidation and DIESEL tests depends on the Pt and Pd precursors, their individual loadings and their ratio (Pt/Pd). For a selected Pt precursor at its content 0.17g/L, the catalytic performance of Pt–Pd–MnOx–Al2O3 catalyst improves with an increase in Pd loading from 0 to 0.35g/L and is nearly constant at a higher Pd loading (0.70g/L). The most active monolithic Pt–Pd–MnOx–Al2O3 catalyst is prepared by using platinum-dinitrodiamine and palladium nitrate solutions as noble metal precursors.The catalytic activity in light hydrocarbon oxidation is shown to correlate with the RedOx properties of PdPt–MnOx–Al2O3 catalysts and the Pt–Pd particle size. The non-additive increase in the catalytic activity of bimetallic catalyst is suggested to connect with a formation of nanoscale PdO–PtOx particles on the surface of Mn3O4 and a modification of alumina structure by Mn3+ and PtPd clusters.

Catalytic activity of bimetallic catalysts highly sensitive to the atomic composition and phase structure at the nanoscale.

The ability to determine the atomic arrangement in nanoalloy catalysts and reveal the detailed structural features responsible for the catalytically active sites is essential for understanding the correlation between the atomic structure and catalytic properties, enabling the preparation of efficient nanoalloy catalysts by design. Herein we describe a study of CO oxidation over PdCu nanoalloy catalysts focusing on gaining insights into the correlation between the atomic structures and catalytic activity of nanoalloys. PdCu nanoalloys of different bimetallic compositions are synthesized as a model system and are activated by a controlled thermochemical treatment for assessing their catalytic activity. The results show that the catalytic synergy of Pd and Cu species evolves with both the bimetallic nanoalloy composition and temperature of the thermochemical treatment reaching a maximum at a Pd : Cu ratio close to 50 : 50. The nanoalloys are characterized structurally by ex situ and in situ synchrotron X-ray diffraction, including atomic pair distribution function analysis. The structural data show that, depending on the bimetallic composition and treatment temperature, PdCu nanoalloys adopt two different structure types. One features a chemically ordered, body centered cubic (B2) type alloy consisting of two interpenetrating simple cubic lattices, each occupied with Pd or Cu species alone, and the other structure type features a chemically disordered, face-centered cubic (fcc) type of alloy wherein Pd and Cu species are intermixed at random. The catalytic activity for CO oxidation is strongly influenced by the structural features. In particular, it is revealed that the prevalence of chemical disorder in nanoalloys with a Pd : Cu ratio close to 50 : 50 makes them superior catalysts for CO oxidation in comparison with the same nanoalloys of other bimetallic compositions. However, the catalytic synergy can be diminished if the Pd50Cu50 nanoalloys undergo phase segregation into distinct chemically-ordered (B2-type) and disordered (fcc-type) domains. This finding is significant since it provides a rational basis for streamlining the design and preparation of Pd-based nanoalloy catalysts in terms of atomic structure and phase state.

HDS and HDN activity of (Ni,Co)Mo binary and ternary nitrides prepared by decomposition of hexamethylenetetramine complexes

Highly dispersed pure phases of binary and ternary nitrides (Co,Ni)Mo were prepared using decomposition of hexamethylenetetramine (HMTA) complexes. Their catalytic activity was evaluated in the HDS of thiophene and HDN of quinoline. Three different pre-treatment modes were applied, including direct in situ preparation of nitrides in the catalytic reactor; pre-sulfidation with hydrogen sulfide and soft oxidation in air followed by sulfidation. Pure bimetallic nitrides are highly active HDN catalysts in the absence of sulfur and show substantial synergy effect between Ni or Co and Mo. By contrast, no synergy was observed for thiophene HDS, specific surface rates for binary and ternary nitrides being similar to that of unsupported MoS 2. Transmission microscopy, XRD and XPS studies showed that MoS 2 segregation on the surface occurs during HDS reaction or sulfidation with H 2S. As a result bimetallic catalysts contained nitride particles covered with MoS 2 layers and VIII group metal sulfide crystalline particles in the subsurface layer. The introduction in the preparation sequence of an additional step of oxidation–sulfidation led to a considerable increase of HDS catalytic activity of bimetallic catalysts. Pre-sulfidation of nitrides with H 2S/H 2 mixture resulted in a drastic decrease of specific surface area (Ssp) and very low HDS activity. Soft sulfidation with thiophene under reaction conditions led to high Ssp and high HDS activity per unit of mass.

Influence of the phase composition of the support on the catalytic activity of bimetallic catalysts

The influence of the nanocrystalline structure of an aluminum-zinc spinel support on the catalytic activity of bimetallic Pt-Sn catalysts in dehydrogenation of 2-methylbutane was studied. The formation of the spinel structure in solid-phase reactions of aluminum and zinc oxides was examined.

Solvent-free aerobic oxidation of benzyl alcohol over Pd monometallic and Au–Pd bimetallic catalysts supported on SBA-16 mesoporous molecular sieves

Pd monometallic and Au–Pd bimetallic catalysts supported on surface-functionalized SBA-16 were prepared by a conventional adsorption method and were examined using X-ray diffraction, nitrogen physisorption, UV–vis spectroscopy, and high-resolution transmission microscopy. SBA-16 with the unique “super-cage” structure effectively controlled the formation of dispersed noble metal nanoparticles in the mesoporous channels. These confined nanoparticles with a narrow particle size distribution exhibited excellent catalytic activity in the solvent-free benzyl alcohol selective oxidation with molecular oxygen. Amine-functionalization remarkably improved the selectivity towards benzaldehyde. Au–Pd bimetallic catalysts showed enhanced catalytic performance compared to the Au and Pd monometallic catalysts. The highest turnover frequency of 8667 h −1 was achieved over a bimetallic catalyst with Au:Pd molar ratio of 1:5; this good catalytic activity can be maintained after five recycling runs. The characterization results of scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy revealed that the bimetallic catalyst was constructed of uniformly alloyed nanoparticles with Pd cluster-on-Au cluster structure. The synergetic effect between Au and Pd nanocluster was suggested to account for the better catalytic activity of bimetallic catalysts because the size-dependent effect can be ruled out due to the effective confinement of noble metal nanoparticles by SBA-16 mesostructure.

The role of Fe addition on the activity of Pd-containing catalysts in multiphase hydrodechlorination

Multiphase hydrodechlorination of 1,4-dichlorobenzene, hexachlorobenzene and 2,4,8-trichlorodibenzofurane was studied in the presence of Pd/C and Pd-Fe/C catalysts. The effect of the addition of a second metal to Pd/C was investigated. The content (1–12 wt.%) and ratio of metals were varied to determine their influence on catalytic activity, which was demonstrated to strongly depend on metal ratio in multiphase hydrodechlorination systems. Metal–metal interaction and structure of bimetallic particles were studied by magnetic measurements and TPR analysis. Bimetallic particles consisted of Pd-enriched PdFe alloy. Also Fe 2O 3 was presented on the surface of catalyst. Based on catalytic performance, magnetic measurements, and TPR, two aspects of the influence of iron addition were considered: (1) formation of Pd-enriched PdFe alloy, which resulted in an increase of catalytic activity of bimetallic catalysts in comparison with Pd/C; (2) formation of FeCl 3 under HDC reaction condition, which prevented complete chlorination of palladium, possibly leading to its deactivation.

Noble metal promoted Ni0.03Mg0.97O solid solution catalysts for the reforming of CH4 with CO2

Reforming of CH4 with CO2 to produce syngas was studied over Ni0.03Mg0.97O solid solution catalyst and its bimetallic derivative catalysts which contained small amounts of Pt, Pd or Rh (the atomic ratio M/(Ni + Mg) was about 2 × 10−4, M = Pt, Pd or Rh). It was found that although the Ni0.03Mg{0.97}O catalyst showed an excellent stability and activity at the reaction temperature of 1123 K, it lost its activity completely within 51 h when the reaction temperature was as low as 773 K. However, both the activity and the stability at 773 K were improved significantly by adding Rh, Pt, or Pd. This synergistic effect is rationally explained by the promoted reducibility of Ni. On all these catalysts, the amount of deposited carbon during the reaction was very low, suggesting that carbon deposition was not the main cause of the deactivation. Also, the catalytic activity of bimetallic catalysts increased gradually with the noble metal loading, but after passing through a maximum, it decreased with superfluous addition. The maximum was found to be located at around the atomic ratio of M/(Ni + Mg) ≈ 0.02% (M = Pt, Pd and Rh). This phenomenon could most probably be attributed to the different composition of Pt-Ni alloy particles formed after the reduction.

Rhodium-technetium catalysts in the dehydrogenation of cyclohexane

The catalytic properties of a Rh-Tc/support (γ-Al2O3, SiO2, or MgO) system in the dehydrogenation of cyclohexane have been investigated. A nonadditive increase in the catalytic activity of bimetallic catalysts in comparison with monometallic systems has been established. This effect depends on the ratio of the amounts of the supported metals and on the nature of the support. Diffuse reflectance spectra showed the presence of ionic forms of the metals in the bimetallic catalysts. Analysis of the catalytic and optical properties allowed one to draw the conclusion that the synergistic effect is explained by the formation of RhxTcy clusters.

Bimetallic catalysts: structure and reactivity

The effect of the support in constraining the formation and defining the structure of bimetallic particles has been considered. Alumina and NaY zeolite supported platinum and cobalt bimetallic catalysts are illustrated to rationalize this effect. The surface composition and dispersion of the bimetallic particles are further correlated with the catalytic activity of bimetallic catalysts in CO hydrogenation.

The role of palladium in dehydrogenation of cyclohexane over PtPd/Al 2O 3 bimetallic catalysts

Supported catalysts of platinum, palladium and platinum-palladium/Al 2O 3 with metallic contents from 1.0 to 0.2% were prepared by ion exchange or co-impregnation and physical mixture. The metallic dispersion was determinated by hydrogen-oxygen titration and electron microscopy studies; a good agreement was obtained. The catalytic activity was studied in a conventional flow reactor at low conversions (<1%) to avoid mass and heat transfer limitations. The reaction rate was measured under atmospheric pressure at 160–200 °C with hydrogen flow and with nitrogen as diluent. The activation energy found is 17 kcal/mol. The results obtained show that the catalytic activity of bimetallic catalysts is five times smaller than that of platinum/Al 2O 3 catalysts. These lower activities of bimetallic catalysts, are explained by a mechanism involving hydride coordination by platinum and the competition of palladium to occupy the oxidizing centers on the alumina surface.