Catalysts For Hydrogenation Of Acetylene Research Articles

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.

Pd/Fiber glass and Pd/5% γ-Al2O3/Fiber glass catalysts by surface self-propagating thermal synthesis

The technique of Surface Self-propagating Thermal Synthesis (SSTS) was used to prepare Pd/γ-Al2O3/fiber glass (FG) catalysts for selective liquid-phase hydrogenation of acetylene in the presence of CO. The results of XRD SR analysis (in synchrotron radiation) in combination with the technique of arrested combustion shed new light on the dynamic of phase transformations in the systems under study and variation in the size of diffraction-active crystallites. The catalytic performance of synthesized catalysts was found to be close to that of similar conventionally prepared catalysts. The EXAFS and TEM data afforded to estimate the variation in relative amounts of Pd0 and PdO in synthesized catalysts. In the course of selective hydrogenation, PdO rapidly (<15 min) reduced to Pd0.

Catalytic performance of a Ti added Pd/SiO 2 catalyst for acetylene hydrogenation

A series of Pd/SiO 2 and Pd–Ti/SiO 2 catalysts were prepared by the incipient wetness impregnation method. The catalytic performance for selective hydrogenation of acetylene to ethylene was measured under “high concentration acetylene”, “high space velocity” and “no dilution gas” conditions. The crystal structure and particle size of the catalysts were characterized by the X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), nitrogen physisorption using the BET method and transmission electron microscope (TEM). The results showed that the titanium oxide in Pd–Ti/SiO 2 catalyst was amorphous and the addition of Ti reduced the particle size of Pd significantly. Comparing to the Pd/SiO 2 catalyst, the ethylene yield increased from 64.1% to 88.3% under Pd–Ti/SiO 2 catalytic system.

Room temperature O2 plasma treatment of SiO2 supported Au catalysts for selective hydrogenation of acetylene in the presence of large excess of ethylene

Supported gold nanoparticles have been proven to be active in the hydrogenation of the acetylene. In this work, we applied gold nanoparticles supported on silica for the selective hydrogenation of acetylene in excess ethylene that was close to current industrial practices. Amine group surface-functionalized silica was used to absorb the gold precursor AuCl4-, and small size-controlled gold nanoparticles are formed after chemical reduction. For the first time, O2 plasma was employed to remove the APTES grafted on the surface of silica for preparing the highly dispersed gold nanoparticles (∼3nm). The results of IR, TGA, XRD, and TEM showed that O2 plasma working under mild conditions (room temperature and low pressure) can efficiently remove the organic compounds without causing the aggregation of the gold nanoparticles. The plasma-treated catalyst Au/SiO2 gave excellent low-temperature selective catalytic activity in the hydrogenation of acetylene. The effects of the reduction temperatures on the catalytic performances of the Au/SiO2 were investigated. The enhanced performance of gold nanoparticles supported on silica as pretreated by O2 plasma was ascribed to two effects: (1) the small size of the gold nanoparticles supported on silica, (2) the nearly neutral charge on the Au nanoparticle, which is favorable to the activation of hydrogen.

Modified Pd catalysts for the selective hydrogenation of acetylene

This article reviews our previous studies to develop high performance catalysts for acetylene hydrogenation. Ethylene selectivity of Pd catalysts in acetylene hydrogenation was improved by adding Si, metal oxides showing SMSI behavior, and either Ag or Cu as promoters. The promoter effect was further enhanced by maximizing the interactions between Pd and added promoters. Chemical vapor deposition was used for the addition of Si, high-temperature reduction for the SMSI metal oxides, and a surface redox (SR) for Ag and Cu. Si modified the Pd surface geometrically, SMSI metal oxides modified Pd both electronically and geometrically, and Ag modified Pd largely electronically. Cu added by SR modified Pd electronically to a small extent, but preferentially decorated the low-coordination sites of Pd such that the ethylene selectivity of the optimum catalyst was significantly promoted from that of Pd, while its activity remained comparable to that of Pd. The sensitivity of ethylene selectivity to the surface structure of Pd was demonstrated using model catalysts containing uniform-sized Pd particles in either cubic or spherical shapes. The three stage deactivation of the Pd catalyst and the self-regenerative behavior in early stages of deactivation were also investigated.

Performance and regeneration studies of Pd–Ag/Al 2O 3 catalysts for the selective hydrogenation of acetylene

The selective hydrogenation of acetylene is one process to remove traces of acetylene from steam cracker cuts during the production of ethylene. Current disadvantages of commercially used Pd–Ag/Al 2O 3 catalysts applied in the C 2-tail end-selective hydrogenation are relative short cycle time (fast deactivation) caused by green oil formation and deposition of coke. Long-term tests were performed in a laboratory reactor under typical industrial conditions to investigate the deactivation of those catalysts. It was found that the Pd–Ag/Al 2O 3 catalyst with the highest long-term stability contains a Ag/Pd-ratio in the bulk of 0.41 and the lowest concentration of silver. This low silver amount causes a higher dilution of the palladium surface area than the higher silver amount within the investigated catalysts. This was indicated by CO chemisorption experiments, X-ray photoelectron spectroscopy (XPS), electron probe micro analysis (EPMA), X-ray fluorescence spectroscopy (XRF) and through the investigation of hydrocarbons deposited on the catalyst surface. The same catalyst sample was subsequently regenerated and tested in the laboratory reactor with respect to its long-term stability. The regenerated samples have the same long-term stability as the fresh sample if the regeneration procedure includes a hydrogen treatment.

Non-thermal RF plasma effects on surface properties of Pd/TiO2 catalysts for selective hydrogenation of acetylene

Non-thermal RF plasma modification has been applied to Pd/TiO2 catalysts for selective hydrogenation of acetylene in the presence of ethylene. High ethylene selectivity and high acetylene conversion were obtained over 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), Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) with CO and temperature-programmed desorption with ethylene (C2H4-TPD). XPS and H2-DSC results confirmed that supported Pd precursors could be effectively reduced to the metallic state during the room temperature plasma treatment. Plasma treatments also enhanced the surface active sites of Pd/TiO2 catalysts and improved the dispersion of Pd metal particles. In addition, DRIFTS and C2H4-TPD results indicated that plasma treatments could induce strong metal-support interaction with lower reduction temperature (200°C), which lead to an enhanced catalytic performance on selective hydrogenation of acetylene. It demonstrates that the RF non-thermal plasma treatment is an effective way to manipulate surface properties and the interaction between metals and supports of supported Pd catalysts for selective hydrogenation.

Selective hydrogenation of acetylene on Nanosized catalysts

The use of unconventional methods for the preparation of Nanosized catalysts for the selective hydrogenation of acetylene and its homologs is considered. Based on published data and experimental data obtained in this work, it is shown that catalysts based on nanoparticles of palladium have a high activity, although their selectivity and stability are low. Bimetallic palladium-containing systems are more promising. The most interesting of them are nanocomposites containing palladium and silver or palladium and zinc particles. Another method that makes it possible to increase the selectivity and stability of the catalysts for the hydrogenation of triple bonds is the use of synergism in gold-nickel nanocomposites. The preparation of nanosized hydrogenation catalysts by a recently developed method of laser electrodispersion is considered. This method makes it possible to prepare catalysts with a very narrow distribution of nanoclusters over sizes and with very high specific activity and stability.

Palladium–gallium intermetallic compounds for the selective hydrogenation of acetylene: Part II: Surface characterization and catalytic performance

The structurally well-defined intermetallic compounds PdGa and Pd 3Ga 7 constitute suitable catalysts for the selective hydrogenation of acetylene. The surface properties of PdGa and Pd 3Ga 7 were characterized by X-ray photoelectron spectroscopy, ion scattering spectroscopy and CO chemisorption. Catalytic activity, selectivity and long-term stability of PdGa and Pd 3Ga 7 were investigated under different acetylene hydrogenation reaction conditions, in absence and in excess of ethylene, in temperature-programmed and isothermal long-term experiments. Chemical treatment with ammonia solution—performed to remove the gallium oxide layer introduced during the milling procedure from the surface of the intermetallic compounds—yielded a significant increase in activity. Compared to Pd/Al 2O 3 and Pd 20Ag 80 reference catalysts, PdGa and Pd 3Ga 7 exhibited a similar activity per surface area, but higher selectivity and stability. The superior catalytic properties are attributed to the isolation of active Pd sites in the crystallographic structure of PdGa and Pd 3Ga 7 according to the active-site isolation concept.

Identification of Non-Precious Metal Alloy Catalysts for Selective Hydrogenation of Acetylene

The removal of trace acetylene from ethylene is performed industrially by palladium hydrogenation catalysts (often modified with silver) that avoid the hydrogenation of ethylene to ethane. In an effort to identify catalysts based on less expensive and more available metals, density functional calculations were performed that identified relations in heats of adsorption of hydrocarbon molecules and fragments on metal surfaces. This analysis not only verified the facility of known catalysts but identified nickel-zinc alloys as alternatives. Experimental studies demonstrated that these alloys dispersed on an oxide support were selective for acetylene hydrogenation at low pressures.

Promotion Effects of Air and H2 Nonthermal Plasmas on TiO2 Supported Pd and Pd−Ag Catalysts for Selective Hydrogenation of Acetylene

Selective hydrogenation of acetylene in rich ethylene was investigated over uncalcined, air plasma, and H2 plasma Pd/TiO2 and Pd−Ag/TiO2 catalysts. Air and H2 plasma treatments have different modifying effects on Pd/TiO2 catalyst for selective hydrogenation of acetylene to ethylene. With additional Ag loadings, 1% and 3%, on Pd/TiO2, plasma treatments shift the temperature of maximum C2H4 yield to lower temperatures as compared to Ag shifting the maximum yield temperature to higher temperatures. Air plasma treatment alone on Pd/TiO2 produces the highest maximum C2H4 yield at the lowest temperature among all catalysts tested. H2 plasma, on the other hand, is more effective in enhancing the performance of the Pd−1%Ag/TiO2 catalyst. Both air and H2 plasmas show the capability to shift the maximum yield temperatures of Pd/TiO2 and Pd−Ag/TiO2 catalysts to lower temperatures. It provides a new avenue to fine-tune the catalytic reactivity of supported Pd catalysts with or without the Ag promoter to selectively convert acetylene to ethylene in excess of ethylene to meet various industrial demands.

Effect of Ag addition on the properties of Pd–Ag/TiO2 catalysts containing different TiO2 crystalline phases

Anatase and rutile TiO2 were used for preparation of the TiO2 supported Pd and Pd–Ag catalysts for selective hydrogenation of acetylene. It was found that Pd/TiO2-anatase exhibited higher acetylene conversion and ethylene selectivity than rutile TiO2 supported ones. However, addition of Ag to Pd/TiO2-anatase catalyst resulted in lower ethylene selectivity while that of Pd/TiO2-rutile increased. It is suggested that Ag addition suppressed the beneficial effect of the Ti3+ sites presented on the anatase TiO2 during selective acetylene hydrogenation whereas without Ti3+, Ag promoted ethylene selectivity by blocking sites for over-hydrogenation of ethylene to ethane.

Preparation of novel titania supported palladium catalysts for selective hydrogenation of acetylene to ethylene

Novel titania supports have been designed and elaborated with the hydrolysis precipitation method, by adjusting and controlling of the main preparation parameters, such as pH value, adding rate of tetrabutyl titanate Ti(OBu)4, and calcining temperature of precursor during support preparation. The new titania supported Pd catalysts were prepared and investigated for selective hydrogenation of acetylene to ethylene. The catalyst samples have been characterized by temperature programmed reduction (TPR), XRD and BET techniques. The experimental results indicated that with MgO modification, the improved catalyst (0.5%Pd–MgO/TiO2) showed better performance of high and stable activity.

Nonthermal RF Plasma Modifications on Pd/γ-Al2O3 for Selective Hydrogenation of Acetylene in the Presence of Ethylene

Nonthermal RF plasma modification has been applied to alumina-supported Pd catalysts for selective hydrogenation of acetylene in the presence of ethylene. High ethylene selectivity and good acetyle...

Catalytic Properties of Supported Pd/TiO&lt;sub&gt;2&lt;/sub&gt; and Pd-Ag/TiO&lt;sub&gt;2&lt;/sub&gt; Catalysts for Selective Hydrogenation of Acetylene

Catalytic Properties of Supported Pd/TiO&lt;sub&gt;2&lt;/sub&gt; and Pd-Ag/TiO&lt;sub&gt;2&lt;/sub&gt; Catalysts for Selective Hydrogenation of Acetylene

Surface characterisation of Pd–Ag/Al 2O 3 catalysts for acetylene hydrogenation using an improved XPS procedure

Effects of pretreatment on the surface of alumina-supported Pd–Ag catalysts with oxygen or oxygen-containing compounds (NO, N 2O, CO and CO 2) have been studied using an improved X-ray photoelectron spectroscopy (XPS). Surface analysis was performed either before or after the selective hydrogenation of acetylene. Analysis of the surface after reduction shows evidence of a Pd–Ag alloy. The binding energy of the Pd 3d is not affected by pretreatment, whereas a significant shift of the Ag 3d is revealed after NO and N 2O pretreatment. The surface after reaction shows no state change of either Pd or Ag compared to those measured prior to reaction, which is in agreement with the reactivity test; therefore surface modification occurs after pretreatment and is retained even after 8 h on stream. No carbonaceous deposits are formed after 8 h on stream. Ethylene gain enhancement by NO and N 2O pretreatment is a result of strong adsorption on the surface which may block the sites responsible for ethylene hydrogenation without facilitating carbonaceous deposits for hydrogen spillover. On the other hand, pretreatment with O 2, CO or CO 2 increases the Pd active sites, which increases C 2H 2 hydrogenation activity.

Plasma torch generation of carbon supported metal catalysts

Novel plasma torch generated Pd/C, and PdAg/C catalysts were tested for reactivity for two hydrogenation reactions and characterized using a number of techniques. The general conclusion reached was that the metal catalysts created in this fashion were extremely highly dispersed (>50% in some cases) and had concomitantly high activity on a gram basis. The PdAg/C catalysts exceeded the selectivity of PdAg/Al 2O 3 catalysts for selective hydrogenation of acetylene. The selectivity of Pd/C catalysts for 1-butene isomerization was equal or better than that of catalysts prepared by conventional means, and the activity nearly as high. One surprise was the finding that plasma generated PdAg/C catalysts had no apparent activity for 1-butene isomerization. A second surprise was the finding that the plasma treatment did not increase the crystallinity of the carbon but did result in the loss up to 30% of the surface area.

Effect of Ag‐promotion on Pd catalysts by XANES

Pd L3 near‐edge absorption measurements (XANES) were performed on four commercial acetylene hydrogenation catalyst samples, with and without the Ag promoter. The Pd L3 edge XANES spectra showed that the Ag‐promoted catalysts have relatively weaker absorption peaks and they follow the same order as the relative commercial performances of the four catalysts studied in terms of selectivity in ethylene purification, which indicates that there are increases in the Pd d‐band electron densities due to the addition of Ag. These results provide a reasonable explanation for the observed improvement in selectivity of the Ag‐promoted acetylene hydrogenation catalysts. The Ag L3 XANES spectra of the supported Pd–Ag catalysts indicate the absence of a white‐line feature which seems to suggest that the charge transferred from Ag to Pd may not be the d‐type.

Effect of Zn Content on Catalytic Activity and Physicochemical Properties of Ni-Based Catalysts for Selective Hydrogenation of Acetylene

The influence of zinc addition on the catalytic performance andphysicochemical properties of nickel-based catalysts used inselective hydrogenation of acetylene was investigated. It was foundthat the activity and selectivity to ethylene of the nickel-basedcatalysts were positively modified by incorporation of zinc intotheir solid structure. The zinc-modified catalysts produced smalleramounts of coke and methane than those not containing zinc. Cokedeposition had a strong effect on the ethylene selectivity.However, this influence was much more significant for zinc-modifiedcatalysts than for nonmodified nickel-based solids. These resultswere explained taking into account the different crystallinestructures obtained for both types of solid. In the case ofzinc-modified catalysts, the metal nickel phase was interactingstrongly and highly interdispersed in a nonstoichiometric zincaluminate spinel matrix. The high interdispersion of the metal nickelphase diminished the number of three-nickel-atom arrangementsnecessary for the formation of surface intermediates that led to cokeand methane production. The nonmodified nickel-based solids, however,were composed of large metal crystallites on which coke and methaneprecursors were very easily formed. The high interaction betweenmetal nickel particles and the zinc aluminate matrix preventedwhisker formation to some extent. Finally, the low concentration ofacid sites on the solid surface considerably reduced amorphous-likecoke deposition.

Incorporation of Deuterium in Coke Formed on an Acetylene Hydrogenation Catalyst

Researchers have been attempting to characterize heterogeneous catalysts in situ in addition to correlating their structures with their activity and selectivity in spite of many challenges. Here, we review recent experimental and theoretical advances regarding alkyne selective hydrogenation by Pd-based catalysts, which are an important petrochemical reaction. The catalytic selectivity for the reaction of alkynes to alkenes is influenced by the composition and structure of the catalysts. Recent progress achieved through experimental studies and atomic simulations has provided useful insights into the origins of the selectivity. The important role of the subsurface species (H and C) was revealed by monitoring the catalyst surface and the related catalytic performance. The atomic structures of the Pd catalytic centers and their relationship with selectivity were established through atomic simulations. The combined knowledge gained from experimental and theoretical studies provides a fundamental understanding of catalytic mechanisms and reveals a path toward improved catalyst design.