Pilot tests of a catalyst for the selective hydrogenation of acetylene

Pilot tests of SGA-2M promoted Pd/Al₂O₃ catalyst in the selective hydrogenation of acetylene are performed on an industrial ethane-ethylene fraction in a system of two serially arranged adiabatic flow reactors. The optimum process conditions under which the conversion of acetylene reaches 100% at a selectivity of 68.2% with respect to ethylene are determined: system pressure, 21 atm; hydrocarbon feedstock hourly space velocity (HSV), 1500 h^?1, carbon monoxide concentration, 7 ppm; H₂: C₂H₂ molar ratio at the first and second hydrogenation stages, 1.0: 1.0 and 1.4: 1.0; inlet temperature of the first and second reactors, 40 and 55°C, respectively. The interregeneration service life of the SGA-2M catalyst under optimum conditions is estimated at 12 months. SGA-2M catalysts can be recommended for purifying ethane-ethylene fractions containing up to 2 vol % of acetylene.     

Preparation of Pdshell–Aucore/SiO2 catalyst and catalytic activity for acetylene hydrogenation

Various Pd shell thicknesses (0.12–1.5 nm) were synthesized on preformed Au particles of 5 nm size by seeded growth technique (15–80 at% Pd) using sodium citrate and tannic acid. The sols were characterized by UV–vis spectroscopy, TEM and high-resolution TEM (HRTEM) measurements. HRTEM confirmed the pseudomorphic growth of the Pd shell on the Au core. The Au/Pd core/shell particles were fixed onto SiO₂ (Aerosil 200) support by PDDA polycation. The catalytic activity in acetylene hydrogenation and selectivity of competition between acetylene and propene were tested after O₂ and H₂ pretreatment. The samples even in “as prepared” state hydrogenated acetylene. The thin Pd layer (15–30 at% Pd) on Au provided higher hydrogenation activity than the thick Pd shell. However, thermal treatment of the samples in H₂ stream causing Au/Pd intermixing shifted the activity maximum to higher Pd concentration (68–80 at% Pd). Comparison of the TOF (1/s) and selectivity values allowed us to conclude that the homogenized particle with 68–80 at% Pd shows better hydrogenation activity and selectivity than the thin Pd shell (15–30 at% Pd) on the Au core.     

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.     

Catalytic performance of a Ti added Pd/SiO2 catalyst for acetylene hydrogenation

A series of Pd/SiO₂ and Pd–Ti/SiO₂ 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/SiO₂ catalyst was amorphous and the addition of Ti reduced the particle size of Pd significantly. Comparing to the Pd/SiO₂ catalyst, the ethylene yield increased from 64.1% to 88.3% under Pd–Ti/SiO₂ catalytic system.     

Modification of the catalytic properties of supported noble metal catalysts by carrier doping

The influence of altervalent cation doping of TiO₂ carriers on the chemisorptive and catalytic properties of supported Pt and Rh crystallites has been investigated. It was observed that doping of the carrier with higher valence cations leads to suppression of the H₂ and CO chemisorption capacity of Pt catalysts, while their activity in hydrogenation and oxidation reactions is significantly reduced. The opposite effects were observed in the case of Rh catalysts supported on higher valence doped TiO₂. These catalysts were found to possess higher activity in CO and CO₂ hydrogenation, in aromatics hydrogenation and in CO and C₂H₄ oxidation. Their stability characteristics were also found to be superior to those of the undoped Rh/TiO₂ catalyst. These effects are believed to originate from an electronic type interaction at the metal-support interface, induced by doping, which results in electron transfer from the support to the metal crystallites.     

Performance of Pd–Ag/Al2O3 catalysts prepared by the selective deposition of Ag onto Pd in acetylene hydrogenation

The performance of Ag-promoted Pd/Al₂O₃ catalysts, which were prepared by the selective deposition of Ag onto Pd using a surface redox (SR) method, during acetylene hydrogenation was compared with that of catalysts prepared by impregnation. The Pd surface was more effectively modified with Ag added by SR, even when small amounts of Ag were added. The catalyst prepared by SR showed a higher ethylene selectivity than the one prepared by impregnation, because SR allowed both the preferential deposition of Ag on the low-coordination sites of Pd and a greater electronic modification of Pd by Ag.     

原位红外光谱法研究Pd-Ag/Al2O3和Pd/ Al2O3乙炔加氢催化剂

以一氧化碳和乙炔为探针分子,采用原位红外光谱技术研究了Pd-Ag/ Al₂O₃和Pd/ Al₂O₃催化剂上乙炔加氢反应以及催化剂本身的表面形态,动态考察了乙炔加氢的气相反应行为、CO吸附以及催化剂表面吸附物种的变化。结果表明,在Pd-Ag/ Al₂O₃催化体系中,由于Ag的加入而受到几何效应和电子效应的共同影响,引起了催化剂表面形态的改变从而改变了催化剂的性能。另外,乙炔加氢反应会导致钯催化剂表面形成由长分子链的饱和烃组成的碳氢化合物层,该碳氢化合物层有可能是加氢反应形成的绿油。     

Benzyltitanium- und -zirconium/Al2O3-Katalysatoren zur partiellen Hydrierung von Acetylen

Benzyl Titanium and Zirconium Alumina Catalysts for Partial Hydrogenation of Acetylene Benzyl titanium and zirconium compounds of the types Bzl₄M, C₅H₅MBzl₃, and (C₅H₅)₂MBzl₂ form surface compounds on dehydroxylated alumina (15% α-, and 85% δ-Al₂O₃) which on hydrogenolysis yield TiH- and ZrH-species. The supported systems were studied with respect to catalytic activity in the partial hydrogenation of acetylene. Supported (C₅H₅)₂TiBzl₂ was proved to be inactive and the systems C₅H₅TiBzl₃(Al₂O₃) and Bzl₄/Al₂O₃ catalyze the formation of polyacetylene, but catalysts containing benzyl zirconium species are suitable for the partial hydrogenation of acetylene. Acitivity and selectivity of the system C₅H₅ZrBzl₃/Al₂O₃ are comparable to industrial used Pd/Al₂O₃ catalysts.     

Hydrogenation of methyl sorbate and soybean esters with polymer-bound metal catalysts

New polymer-bound hydrogenation catalysts were made by complexing PdCl₂, RhCl₃·3H₂O, or NiCl₂ with anthranilic acid anchored to chloromethylated polystyrene. The Pd(II) and Ni(II) polymers were reduced to the corresponding Pd(O) and Ni(O) catalysts with NaBH₄. In the hydrogenation of methyl sorbate, these polymer catalysts were highly selective for the formation of methyl 2-hexenoate. The diene to monoene selectivity decreased in the order: Pd(II), Pd(O), Rh(I), Ni(II), Ni(O). Kinetic studies support 1,2-reduction of the Δ4 double bond of sorbate as the main path of hydrogenation. In the hydrogenation of soybean esters, the Pd(II) polymer catalysts proved superior because they were more active than the Ni(II) polymers and produced lesstrans unsaturation than the Rh(I) polymers. Hydrogenation with Pd(II) polymers at 50~100 C and 50 to 100 psi H₂ decreased the linolenate content below 3% and increasedtrans unsaturation to 10~26%. The linolenate to linoleate selectivity ranged from 1.6 to 3.2. Reaction parameters were analyzed statistically to optimize hydrogenation. Recycling through 2 or 3 hydrogenations of soybean esters was demonstrated with the Pd(II) polymers. In comparison with commercial Pd-on-alumina, the Pd(II) polymers were less active and as selective in the hydrogenation of soybean esters but more selective in the hydrogenation of methyl sorbate. Presented at ISF-AOCS Meeting, New York, April 1980.     

Pd@C3N4 nanocatalyst for highly efficient hydrogen storage system based on potassium bicarbonate/formate

Formate/bicarbonate system has several desirable properties such as noncorrosive and nonirritating nature, as well as facile handling, which make it an attractive candidate for a safe, reversible hydrogen storage material. Herein, Pd nanoparticles supported on mesoporous graphitic carbon nitride (mpg‐C₃N₄) for formate‐based reversible hydrogen storage is reported. The as‐developed Pd/mpg‐C₃N₄ material was shown to be a superior catalyst for the hydrogenation of high concentrations of bicarbonate to formate under mild conditions. The effects of reaction temperature, H₂ pressure, and bicarbonate concentration on the hydrogenation of bicarbonate to formate were investigated. The catalytic performance remained steady with high activity up to six hydrogenation cycles. The interaction between mpg‐C₃N₄ and Pd nanoparticles and the concerted effects of the nitrogen species located at mpg‐C₃N₄ and bicarbonate played a synergetic role in the enhancement of the performance of the catalyst for hydrogenation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2410–2418, 2016     

Partial oxidation of unsaturated hydrocarbons over Pd(111): Oxygen scavenging of reactive intermediates and the formation of furan from C2H2 and C4H4

Furan is formed by selective oxidation of both C₂H₂ and C₄H₄ over Pd(111). In the former case, oxygen scavenging of reactively formed C₄H₄ directly demonstrates that this species is the key intermediate in acetylene cyclotrimerisation. In the latter case, overall selectivity towards furan formation can be as high as 80%.     

Palladium Containing Catalysts Based on Hypercrosslinked Polystyrene for Selective Hydrogenation of Acetylene Alcohols

This paper reports palladium nanoparticle formation and stabilization by hypercrosslinked polystyrene and the catalytic properties of the nanocomposites obtained. The nanocomposites were characterized using low-temperature nitrogen physisorption, X-ray photoelectron spectroscopy and transmission electron microscopy. The inorganic nanoparticle size was found to depend on the Na₂PdCl₄ loading with the smallest nanoparticles formed at 0.1?wt% of Pd. The nanocomposites synthesized showed high activity [up to 27?mol/(mol Pd?s)] and selectivity (up to 98.5?% at 100?% conversion) in selective hydrogenation of acetylene alcohols.     

Selective hydrogenation of acetylene through a short contact time reactor

A novel approach to the selective hydrogenation of acetylene involves a short contact time reactor. A thin Pd/γ-Al₂O₃ catalytic membrane (about 5 μm thick) was observed to be void of minor defects. Forcing a dilute C₂H₂/H₂/Ar mixture through the layer produced high conversions coupled with high selectivity at high temperatures. The selectivity was observed to increase with temperature. A gas-dispersion model with derived kinetics was employed to explain the results. A solution to the corresponding coupled nonlinear differential equations resulted in a Peclet number of 64.5 and a contact time of 9.5 × 10⁻³ s through the reactor at 100°C. A critical thickness is predicted to exist for a maximum in ethylene concentration. A value of 2.5 μm at 200°C is representative. Lastly, permeability experiments agree with modeling results to show that Knudsen diffusion is absent despite a narrow pore-size distribution.     

Effective modification of Pd surfaces with TiO2 promoters using selective chemical vapor deposition and the effect on catalytic performance improvement

In this paper, we describe a novel method for selectively attaching TiO₂ promoters on Pd surfaces in Pd/SiO₂ catalysts using selective chemical vapor deposition (CVD). Ti was selectively deposited on Pd active sites over a SiO₂ support under a hydrogen atmosphere when titanium tetraisopropoxide was used as a Ti precursor. The Pd–Ti/SiO₂ catalyst modified by CVD exhibits approximately 1.8 times higher ethylene selectivity than the un-modified Pd/SiO₂ catalyst in the selective hydrogenation of acetylene due to the effective geometric modification of the Pd surface, which is beneficial to ethylene selectivity, by the selectively deposited Ti species.     

Selective detection of acetylene gas extracted from isolation oil by an electrochemical sensor using a gold electrode

The selective detection of acetylene in gases extracted from isolation oils has been studied to develop an electrochemical sensor for the diagnostic monitoring of the condition of in-service electrical instruments. Effects of coexisting gases (CH₄, C₂H₆, C₂H₄, H₂ and CO) on the oxidation current of C₂H₂ were tested using gas-permeable gold-coated and platinum-black electrodes as the sensor. The gold-coated electrode showed good behaviour for the selective current detection of acetylene under potentiostatic conditions (−0.1 V/Pt-black reference electrode) in 10m H₂SO₄ electrolyte solution.     

Physically and chemically mixed TiO2-supported Pd and Au catalysts: unexpected synergistic effects on selective hydrogenation of citral in supercritical CO2

The selective hydrogenation of citral was studied with various TiO₂-supported monometallic and bimetallic Pd and Au catalysts and their physical mixtures in supercritical CO₂ (scCO₂). Significant synergistic effects appeared when active Pd species was chemically or physically mixed with less active Au species. The total rate of conversion was greatly enhanced and the selectivity to citronellal (CAL) was improved. The physical properties of those catalysts were characterized by TEM, HRTEM-EDS, XPS, and UV/Vis and their features of H₂ desorption were examined by TPD. The physical and chemical characterization results were used to discuss the reasons for the unexpected synergistic effects observed. The same selective hydrogenation was also conducted in a conventional non-polar organic solvent of n-hexane to examine the roles of scCO₂. The use of scCO₂ was effective for accelerating the hydrogenation of citral and improving the selectivity to CAL.     

Model study on the aqueous-phase hydrodechlorination of clopyralid on noble metal catalysts

The aqueous-phase catalytic hydrodechlorination (HDC) of the herbicide clopyralid was studied for the first time. The reaction was carried out on platinum- (Pt), palladium- (Pd) and gold- (Au) based mono- and bimetallic catalysts at 25 °C and atmospheric pressure using a batch reactor. Clopyralid (3,6-dichloropyridine-2-carboxylic acid) is a systemic herbicide from the chemical class of pyridine compounds, which has a high potential to contaminate water sources. The hydrodechlorination of clopyralid (C₆H₃NO₂Cl₂) proceeds step-wise to the monochlorinated intermediates 3-chloropyridine-2-carboxylic acid and 6-chloropyridine-2-carboxylic acid (C₆H₄NO₂Cl) and to the dechlorinated intermediate picolinic acid (C₆H₅NO₂). The dechlorination is followed by hydrogenation with formation of the harmless end product pipecolinic acid (C₆H₁₀NO₂). With different alumina supported mono- and bimetallic catalysts a complete dechlorination and hydrogenation of clopyralid could be achieved. Pd and PdAu catalysts showed the highest activity for the dechlorination steps whereas the Pt and PtAu catalysts are most active in the complete conversion of clopyralid, i.e. combined dechlorination and hydrogenation. Summarizing, HDC is an easily applicable way to remove clopyralid from water.     

Performance of Ni-added Pd-Ag/Al2O3 catalysts in the selective hydrogenation of acetylene

Effects of Ni addition on the performance of Pd-Ag/Al₂O₃ catalysts in the selective hydrogenation of acetylene were investigated. Ni-added Pd-Ag catalysts showed higher conversions than Ni-free Pd-Ag catalyst under hydrogen-deficient reaction conditions, hydrogen/acetylene <2.0, due to the spillover of hydrogen from reduced Ni to Pd and the suppression of hydrogen penetration into the Pd bulk phase, which enriched the Pd surface with hydrogen. Ethylene selectivity was also increased by Ni addition because the amounts of surface hydrogen originating from the Pd bulk phase, which was responsible for the full hydrogenation of ethylene to ethane, were decreased due to the presence of Ni at the sub-surface of Pd-Ag particles. Added Ni also modified the geometric nature of the Pd surface by blocking large ensembles of Pd into isolated ones, which eventually improved ethylene selectivity.     

The chemistry of Pd in cellulose acetate

Pd(OAc)₂ complex has been incorporated in cellulose acetate (CA) as a dispersion medium using cosolvent (THF). The interactions Pd(II) complexes and cellulose acetate are examined by infrared spectroscopy and thermal analysis (DSC). The chemical reactivities of Pd–CA films have been investigated by reacting Pd sites with CO, H₂, O₂, and C₂H₄ in the temperature range 25–150°C and at the pressure of less than 1 atm. Two different Pd-carbonyls and a Pd(O)-hydride species formed in CA are characterized by their infrared spectra. Treatment of 10 wt % Pd–CA films with hydrogen (600 torr) at 70°C produces small Pd metal particles of ca. 30–60 Å in diameter in CA, which show catalytic activities under mild conditions in the reactions such as hydrogenation of C₂H₄ and oxidation of CO.     

Diamond-like carbon thin films by microwave surface-wave plasma CVD aimed for the application of photovoltaic solar cells

The nitrogen doped diamond-like carbon (DLC) thin films were deposited on quartz and silicon substrates by a newly developed microwave surface-wave plasma chemical vapor deposition, aiming the application of the films for photovoltaic solar cells. For film deposition, we used argon as carrier gas, nitrogen as dopant and hydrocarbon source gases, such as camphor (C₁₀H₁₆O) dissolved with ethyl alcohol (C₂H₅OH), methane (CH₄), ethylene (C₂H₄) and acetylene (C₂H₂). The optical and electrical properties of the films were studied using X-ray photoelectron spectroscopy, Nanopics 2100/NPX200 surface profiler, UV/VIS/NIR spectroscopy, atomic force microscope, electrical conductivity and solar simulator measurements. The optical band gap of the films has been lowered from 3.1 to 2.4 eV by nitrogen doping, and from 2.65 to 1.9 eV by experimenting with different hydrocarbon source gases. The nitrogen doped (flow rate: 5 sccm; atomic fraction: 5.16%) film shows semiconducting properties in dark (i.e. 8.1 × 10^{− 4} Ω^{− 1} cm^{− 1}) and under the light illumination (i.e. 9.9 × 10^{− 4} Ω^{− 1} cm^{− 1}). The surface morphology of the both undoped and nitrogen doped films are found to be very smooth (RMS roughness ≤ 0.5 nm). The preliminary investigation on photovoltaic properties of DLC (nitrogen doped)/p-Si structure show that open-circuit voltage of 223 mV and short-circuit current density of 8.3 × 10^{− 3} mA/cm². The power conversion efficiency and fill factor of this structure were found to be 3.6 × 10^{− 4}% and 17.9%, respectively. The use of DLC in photovoltaic solar cells is still in its infancy due to the complicated microstructure of carbon bondings, high defect density, low photoconductivity and difficulties in controlling conduction type. Our research work is in progress to realize cheap, reasonably high efficiency and environmental friendly DLC-based photovoltaic solar cells in the future.