Catalysts For Hydrogenation Of Acetylene Research Articles

Characterization and performance of Pd/Ni(Zn)-aluminate catalysts for acetylene hydrogenation

0.03 wt% Pd catalysts on nickel and zinc aluminate supports were prepared by impregnation. The samples were characterized by XRD, BET, ICP, SEM, EDS, CO-TPD, NH3-TPD, and their performances were evaluated in an acetylene selective hydrogenation reaction. The Ni2Al18O29, NiAl26O40 and NiAl2O4 structures for nickel aluminates and ZnAl2O4 and Zn4Al22O37 structures for zinc aluminates were identified in supports. The specific surface area of aluminateswere in the range of 46.7–87.5 m2/g. Surface acidity of the support was in the order nickel aluminate < zinc aluminate < θ, δ-alumina. CO-TPD analysis showed that most of Pd active sites on the aluminate support were in multicoordination forms. The nickel and zinc aluminates had lower acetylene conversion than theta and delta alumina.

Variability of particle configurations achievable by 2-nozzle flame syntheses of the Au-Pd-TiO2 system and their catalytic behaviors in the selective hydrogenation of acetylene

Catalysts with Au and Pd supported on TiO2 (Au:Pd 1:1wt/wt%) were prepared by 1- and 2-nozzle flame spray pyrolysis (FSP). The 2-nozzle configuration allowed to synthesize various particle configurations by separate or co-feeding of the metal precursor solutions to the two nozzles. For the Au-Pd/TiO2 system, four different catalyst particle configurations were investigated: “TiO2+AuPd”, “Pd/TiO2 +Au”, “Au/TiO2 +Pd”, and “Pd/TiO2+Au/TiO2”, where+separates the corresponding precursor solutions fed to the two nozzles. There were no significant differences in the specific surface areas and the average TiO2 crystallite sizes of the catalysts (100m2/g and 16–17nm, respectively) with the exception of “Pd/TiO2 +Au/TiO2”, which exhibited larger surface area and smaller crystallite size (152m2/g, 12nm) due to halving of the Ti precursor concentration in each nozzle. As revealed by CO chemisorption, XPS, and STEM-EDX results, the catalyst properties varied largely in terms of bimetallic AuPd particle compositions, the interaction between metal–metal and metal-support, and the location of Pd (or AuPd) on the TiO2. Among the catalysts studied, “TiO2+AuPd” prepared with the 2-nozzle system exhibited the highest conversion of acetylene (∼50%) at 40°C with high selectivity to ethylene (>95%). Co-feeding the noble metal precursors together with the Ti precursor afforded less active catalysts due to the formation of Ti-O species partially covering the most active bimetallic AuPd particles. Compared to the commercially available acetylene hydrogenation catalyst and the AuPd/TiO2 prepared by conventional co-impregnation and deposition-precipitation, all the FSP-AuPd/TiO2 catalysts showed superior performances under the reaction conditions used.

Layered Double Hydroxides Derived ZnO‐Al2O3 Supported Pd‐Ag Catalysts for Selective Hydrogenation of Acetylene

AbstractZnO‐Al2O3 derived from layered double hydroxides (ZnAl‐LDH) was successfully applied for dispersion of Pd‐Ag bimetallic catalysts for the selective hydrogenation of acetylene to ethylene and the Pd‐Ag/ZnO‐Al2O3 catalyst showed the best catalytic performance among the prepared samples. It was found that the catalyst carrier of ZnO‐Al2O3 metal‐oxides derived form ZnAl‐LDH could significantly suppress the over‐hydrogenation of acetylene to obtain the relatively higher selectivity of ethylene. The introduction of Ag restricted efficiently the formation of coke because of the oligomerization reaction, which was further evidenced by thermal gravimetric analysis. The selectivity towards ethylene was in the order of Pd‐Ag/ZnO‐Al2O3&gt;Pd/ZnO‐Al2O3&gt;Pd‐Ag/Al2O3&gt;Pd/Al2O3 at a high conversion level. As the thermal gravimetric and differential temperature analysis (TG‐DTA) revealed, Pd‐Ag intermetallic catalyst on the ZnO‐Al2O3 support showed less coke formation.

Selective Hydrogenation of Acetylene Over Pd/Al2O3 Catalysts: Effect of Non-thermal RF Plasma Preparation Methodologies

Supported palladium nanocatalysts have been reported to be active in selective hydrogenation of acetylene. In this work, non-thermal radio frequency plasma modification has been applied to Pd/Al2O3 catalysts for selective hydrogenation of acetylene in the presence of excess ethylene. High ethylene selectivity, good acetylene conversion activity and high TOF were obtained on the plasma-treated catalysts. To understand the plasma effect, the catalysts were characterized by differential scanning calorimetry in hydrogen (H2-DSC), pulse H2 chemisorption, X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption with ethylene (C2H4-TPD) experiments. XPS and H2-DSC results confirmed that the Pd precursor could be effectively reduced to the metallic state during the room temperature plasma treatment. Plasma treatment also improved the dispersion of Pd particles with strong interaction between Al2O3 support and PdO and Pd nitrate precursors. In addition, C2H4-TPD indicated that plasma treatment could lead to an enhanced catalytic performance on selective hydrogenation of acetylene. It demonstrates that the non-thermal RF plasma treatment is an effective way to manipulate surface properties and the interaction between metals and supports of supported Pd catalysts for selective hydrogenation.

Enhancing both selectivity and coking-resistance of a single-atom Pd1/C3N4 catalyst for acetylene hydrogenation

Selective hydrogenation is an important industrial catalytic process in chemical upgrading, where Pd-based catalysts are widely used because of their high hydrogenation activities. However, poor selectivity and short catalyst lifetime because of heavy coke formation have been major concerns. In this work, atomically dispersed Pd atoms were successfully synthesized on graphitic carbon nitride (g-C3N4) using atomic layer deposition. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) confirmed the dominant presence of isolated Pd atoms without Pd nanoparticle (NP) formation. During selective hydrogenation of acetylene in excess ethylene, the g-C3N4-supported Pd NP catalysts had strikingly higher ethylene selectivities than the conventional Pd/Al2O3 and Pd/SiO2 catalysts. In-situ X-ray photoemission spectroscopy revealed that the considerable charge transfer from the Pd NPs to g-C3N4 likely plays an important role in the catalytic performance enhancement. More impressively, the single-atom Pd1/C3N4 catalyst exhibited both higher ethylene selectivity and higher coking resistance. Our work demonstrates that the single-atom Pd catalyst is a promising candidate for improving both selectivity and coking-resistance in hydrogenation reactions.

Pd@C core-shell nanoparticles on carbon nanotubes as highly stable and selective catalysts for hydrogenation of acetylene to ethylene.

Developing highly selective and stable catalysts for acetylene hydrogenation is an imperative task in the chemical industry. Herein, core-shell Pd@carbon nanoparticles supported on carbon nanotubes (Pd@C/CNTs) were synthesized. During the hydrogenation of acetylene, the selectivity of Pd@C/CNTs to ethylene was distinctly improved. Moreover, Pd@C/CNTs showed excellent stability during the hydrogenation reaction.

Catalytic Performance and Characterization of Anatase TiO&lt;sub&gt;2&lt;/sub&gt; Supported Pd Catalysts for the Selective Hydrogenation of Acetylene

Catalytic Performance and Characterization of Anatase TiO&lt;sub&gt;2&lt;/sub&gt; Supported Pd Catalysts for the Selective Hydrogenation of Acetylene

Preparation and structure-property relationships of supported trimetallic PdAuAg catalysts for the selective hydrogenation of acetylene

To simultaneously achieve thorough purification of acetylene and maximum ethene increment, a sea urchinlike trimetallic PdAuAg mesocrystal catalyst as targeting sample and cuboctahedral trimetallic PdAuAgx and bimetallic catalyst as control samples were prepared by a co-reduction method, immobilized on MgAl hydrotalcite. Compared with bimetallic PdAu and PdAg catalysts, trimetallic PdAuAgx catalyst gave prior selectivity due to the positive synergetic effect. Significantly, PdAuAg2 mesocrystal catalyst exhibited a turnover frequency of 0.063s−1, 46.5% higher than that of cuboctahedral PdAuAg2 catalyst. A 76.2% ethene selectivity was achieved for the thorough purification of acetylene over PdAuAg mesocrystal catalyst with H2:C2H2 of 2:1. Further improving H2:C2H2 to 3, 76.5% yield can be maintained at 140°C. Enhanced activity of the mesocrystal catalyst could be attributed to a high concentration of defect sites and a low activation barrier. Improved ethene selectivity could be ascribed to the increase in the (111)/(100) facets ratio and the formation of a Pd-C phase.

Pd/Ga2O3–Al2O3 catalysts for the selective liquid-phase hydrogenation of acetylene to ethylene

The structure of Ga2O3–Al2O3 supports and Pd/Ga2O3–Al2O3 catalysts and the performance of these catalysts in liquid-phase acetylene hydrogenation have been investigated. The deposition of Ga(NO3)3 onto Al2O3 by impregnation followed by calcination of the impregnated support at 600°C yields γ-Ga2O3–Al2O3 solid solutions containing up to 50 wt % Ga2O3. X-ray diffraction characterization of model palladium catalysts and their temperature-programmed reduction with hydrogen have demonstrated that, while palladium in Pd/Ga2O3 is in the form of a Pd2Ga alloy, in the Pd/γ-Ga2O3–Al2O3 catalyst there is no direct interaction between PdО and Ga2O3 particles and palladium is in the monometallic state. The introduction of 10–20 wt % gallium oxide into Al2O3 lowers the activity of the supported palladium catalyst relative to that of the initial Pd/Al2O3 but increases the ethylene yield by enhancing the ethylene formation selectivity.

Investigation of the preparation methodologies of Pd-Cu single atom alloy catalysts for selective hydrogenation of acetylene

Galvanic replacement, co-impregnation and sequential impregnation have been employed to prepare Pd-Cu bimetallic catalysts with less than 1 wt-% Cu and ca. 0.03 wt-% Pd for selective hydrogenation of acetylene in excess ethylene. High angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) and H2 chemisorption results confirmed that Pd-Cu singleatom alloy structures were constructed in all three bimetallic catalysts. Catalytic tests indicated that when the conversion of acetylene was above 99%, the selectivity of ethylene of these three single atom alloy catalysts was still more than 73%. Furthermore, the single atom alloy catalyst prepared by sequential incipient wetness impregnation was found to have the best stability among the three procedures used. Open image in new window

Recent advances in selective acetylene hydrogenation using palladium containing catalysts

Recent advances with Pd containing catalysts for the selective hydrogenation of acetylene are described. The overview classifies enhancement of catalytic properties for monometallic and bimetallic Pd catalysts. Activity/selectivity of Pd catalysts can be modified by controlling particle shape/morphology or immobilisation on a support which interacts strongly with Pd particles. In both cases enhanced ethylene selectivity is generally associated with modifying ethylene adsorption strength and/or changes to hydride formation. Inorganic and organic selectivity modifiers (i.e., species adsorbed onto Pd particle surface) have also been shown to enhance ethylene selectivity. Inorganic modifiers such as TiO2 change Pd ensemble size and modify ethylene adsorption strength whereas organic modifiers such as diphenylsulfide are thought to create a surface template effect which favours acetylene adsorption with respect to ethylene. A number of metals and synthetic approaches have been explored to prepare Pd bimetallic catalysts. Examples where enhanced selectivity is observed are generally associated with decreased Pd ensemble size and/or hindering of the ease with which an unselective hydride phase is formed for Pd. A final class of bimetallic catalysts are discussed where Pd is not thought to be the primary reaction site but merely acts as a site where hydrogen dissociation and spillover occurs onto a second metal (Cu or Au) where the reaction takes place more selectively.

Ag Alloyed Pd Single-Atom Catalysts for Efficient Selective Hydrogenation of Acetylene to Ethylene in Excess Ethylene

Semihydrogenation of acetylene in an ethylene-rich stream is an industrially important process. Conventional supported monometallic Pd catalysts offer high acetylene conversion, but they suffer from very low selectivity to ethylene due to overhydrogenation and the formation of carbonaceous deposits. Herein, a series of Ag alloyed Pd single-atom catalysts, possessing only ppm levels of Pd, supported on silica gel were prepared by a simple incipient wetness coimpregnation method and applied to the selective hydrogenation of acetylene in an ethylene-rich stream under conditions close to the front-end employed by industry. High acetylene conversion and simultaneous selectivity to ethylene was attained over a wide temperature window, surpassing an analogous Au alloyed Pd single-atom system we previously reported. Restructuring of AgPd nanoparticles and electron transfer from Ag to Pd were evidenced by in situ FTIR and in situ XPS as a function of increasing reduction temperature. Microcalorimetry and XANES measurements support both geometric and electronic synergetic effects between the alloyed Pd and Ag. Kinetic studies provide valuable insight into the nature of the active sites within these AgPd/SiO2 catalysts, and hence, they provide evidence for the key factors underpinning the excellent performance of these bimetallic catalysts toward the selective hydrogenation of acetylene under ethylene-rich conditions while minimizing precious metal usage.

EXAFS study of Pd/Sibunit and Pd–Ga/Sibunit catalysts for liquid-phase hydrogenation of acetylene to ethylene

A series of catalysts Pd/Sibunit and Pd–Ga/Sibunit were prepared by impregnation with joint solutions of palladium and gallium nitrates in ethanol. The state of the active component and catalytic properties of the samples were studied in the liquid-phase hydrogenation of acetylene. The EXAFS method showed that the active component in the gallium-modified catalysts exists in the form of a non-stoichiometric Pd–Ga solid solution. The activity of the catalysts was found to be determined by the ratio Pd:Ga. It was shown that at the molar ratios Ga:Pd>0.5:1, the catalytic activity is reduced by blocking the surface of the bimetallic particles by gallium oxide.

Novel Pd–Zn/C catalyst for selective alkyne hydrogenation: Evidence for the formation of Pd–Zn bimetallic alloy particles

The formation of Pd–Zn alloy was revealed in a highly selective Pd–Zn/C catalyst for acetylene hydrogenation prepared via the heterobimetallic PdZn(OAc)4(OH2) complex.

Numerical modelling and performance studies of the original and advanced TEMKIN reactor in laboratory scale testing of industrial egg shell catalysts for the selective hydrogenation of acetylene

Strong interactions between reaction kinetics and transport phenomena force the use of specialised reactors for catalysis experiments. Our working group developed an advanced version of the so called TEMKIN reactor by Temkin and Kulkova (1969), intended for the direct testing of industrial catalysts, e.g. egg shell catalysts used for the selective hydrogenation of acetylene. This work is dealing with modelling of the complex mass and heat transport to investigate and evaluate the influence on the reaction kinetics. Modelling was done using the commercial modelling software COMSOL Multiphysics® and was successfully validated by pulse tagging as well as catalysis experiments. Due to the flexible coupling possibilities in COMSOL, modelling distinguishes between the free gas phase, catalytically active porous shell and inert porous core of the catalyst pellets, ab initio depicting inner as well as outer mass transport limitations. Simulations confirmed good isothermal conditions in both reactor versions, but point out significant transport limitations in the original TEMKIN reactor due to dead zones near the catalyst pellets. Although direct numerical modelling is still challenging due to high computational demands, this work was able to show up its potential in studying laboratory scale reactor designs and catalytic systems.

Stable Au catalysts for selective hydrogenation of acetylene in ethylene

This study investigates the first Au catalysts prepared by photocatalysis process for selective hydrogenation reaction. The photocatalysis process is more straightforward than the encapsulation methods to prepare Au catalysts with small particles. Both 1% and 5%Au/C-TiO2 catalysts were tested for selective hydrogenation of acetylene in ethylene with H2/C2H2 ratios of 2/1, 5/1 and 10/1. With H2/C2H2 ratio of 5/1, both 1% and 5%Au/C-TiO2 catalysts show maximum yields of acetylene conversion to ethylene. Especially, the yield of 1%Au/C-TiO2, after reduction at 250°C, reaches above 80% at temperatures from 200°C to 275°C. Most significantly 1%Au/C-TiO2, after reduction at 250°C with H2/C2H2 ratio of 5/1, is not only active and selective but also stable for selective hydrogenation of acetylene in ethylene. It maintains ∼100% acetylene conversion with ∼80% selectivity to ethylene after 12h at 225°C.

Selective Hydrogenation of Acetylene over Pd–Boron Catalysts: A Density Functional Theory Study

Boron-modified Pd catalysts have shown excellent performance for the selective hydrogenation of alkynes experimentally. In the current work, we investigated the hydrogenation of acetylene on boron-modified Pd(111) and Pd(211) surfaces, utilizing density functional theory calculations. The activity of acetylene hydrogenation has been studied by estimating the effective barrier of the whole process. The selectivity of ethylene formation is investigated from a comparison between the desorption and the hydrogenation of ethylene as well as comparison between the ethylene and the 1,3-butadiene formation. Formation of subsurface carbon and hydrogen on both boron-modified Pd(111) and Pd(211) surfaces has also been evaluated, since these have been reported to affect both the activity and the selectivity of acetylene hydrogenation to produce ethylene on Pd surfaces. Our results provide some important insights into the Pd–B catalysts for selective hydrogenation of acetylene and also for more complex hydrogenation sy...

EXAFS study of model Pd/Ga2O3 catalysts for the liquid-phase hydrogenation of acetylene before and after the reaction

The catalytic characteristics of Pd/Ga2O3 samples in the liquid-phase hydrogenation of acetylene to ethylene are studied. The structure of the catalyst’s components before and after the reaction is examined by EXAFS spectroscopy. The activity of the original (after drying) samples results from the reduction of the original palladium oxide to a metallic state in the reaction medium. According to EXAFS, the catalysts reduced at 200°C contain small amounts of Pd-Ga alloy that was preserved in the reaction medium during the liquid-phase hydrogenation of acetylene and presumably increased the activity and selectivity of the samples.

Performance of shape-controlled Pd nanoparticles in the selective hydrogenation of acetylene

Monodispersed Pd nanoparticles with controlled shapes, either cubes or spheres, were prepared and used as catalysts for acetylene hydrogenation at atmospheric pressure to investigate the effect of the Pd surface structure on the catalytic performance. Catalyst containing cubic Pd nanoparticles, whose surface consisted of the Pd(100) structure, exhibited higher acetylene conversion and ethylene selectivity than catalysts containing spherical nanoparticles, which had a significant amount of Pd(111) facets. These results were consistent with the observation that the temperatures for the decomposition of Pd hydride and the desorption of C2 hydrocarbons from Pd surface were lower for the cubic Pd particles than for the spherical particles. The selectivity of Pd nanocubes was better than that of catalysts containing smaller Pd nanoparticles that were prepared using an incipient wetness method, confirming the importance of the Pd(100) structure in catalyst design for selective acetylene hydrogenation.

TiO2 supported Pd@Ag as highly selective catalysts for hydrogenation of acetylene in excess ethylene

A novel TiO2 supported core-shell (Pd@Ag) bimetallic catalyst was fabricated via the sequential photodeposition method. The Ag shell effectively blocks the high coordination sites on the Pd core, and therefore pronouncedly enhances the ethylene selectivity for the catalytic hydrogenation of acetylene in excess ethylene.