High Acetylene Conversion Research Articles

The Geometric and Electronic Effects of Ceria on Promoting PdZn catalyst for Enhanced Acetylene Semi‐Hydrogenation

AbstractPdZn intermetallic compounds (IMCs) have been extensively reported for acetylene semi‐hydrogenation due to unique geometric and electronic structure of isolated Pd sites. However, to achieve high ethylene selectivity at high conversion remains challenging. Here we show the promotional role of ceria in modifying the geometric and electronic structure of PdZn IMCs towards enhanced catalytic performance for acetylene semi‐hydrogenation. The Ce (0.1 wt%) promoted Pd−Zn‐Al catalyst shows by far the best catalytic performance among other Pd based catalysts in literature, maintaining high selectivity (>95 %) and excellent stability (~130 h) at high acetylene conversion (~90 %). Using in situ spectroscopic techniques, the geometric and electronic effects of CeOx promotor were clearly elucidated. At low Ce content, the presence of highly dispersed Ce3+ species in the periphery of PdZn alloys enhanced electronic metal‐oxide interaction, resulting in electron‐rich Pd sites that promote hydrogen dissociation and ethylene desorption, and account for the outstanding catalytic performance. At high Ce content, the formation of bulk‐phase CeO2 suppressed the PdHx formation during PdZn alloying and led to phase separation yielding highly dispersed Pd ensembles, consequently lowering ethylene selectivity. Our results provide a new route for the design of PdZn catalyst by applying rare earth promoters towards high‐performance acetylene semi‐hydrogenation.

High-efficiency catalysis of Ru-based catalysts assisted by triazine-based ligands containing different heteroatoms (N, O, S) for acetylene hydrochlorination

Ru/AC catalyst used in acetylene hydrochlorination reaction has several drawbacks such as poor dispersion, metal loss, serious carbon deposition, and insufficient active sites. To address these issues of traditional Ru/AC, in this study, the supported Ru-Lx/AC catalysts were synthesized by the coordination of ruthenium precursor and several structural triazine ligands. The complexation of heteroatomic structure to Ru atom formed a local active domain, which is more conducive to the synergistic adsorption and activation of the initial reactants, and further optimizes the reaction microenvironment. The spatial topological structure with conjugated structures effectively promoted the transfer of electrons between the heteroatoms and the ruthenium precursors, facilitating the stabilization of active Ru species. The newly developed synthetic process also increased dispersion of reaction components and impeded the sintering of ruthenium components promoted by the local structural forces. The optimum Ru-1,3,5-triazine/AC (Ru-L1/AC) catalyst exhibited 162% higher acetylene conversion than the benchmark Ru/AC catalyst. The significantly improved activity and stability of the optimized catalyst will have a huge application prospect in industry.

π-Adsorption promoted electrocatalytic acetylene semihydrogenation on single-atom Ni dispersed N-doped carbon

As a novel electrocatalyst for acetylene semihydrogenation, single-atom nickel dispersed N-doped carbon exhibits a high acetylene conversion of 97.4%, which are attributed to weak π-adsorption of ethylene on individual Ni sites.

Breaking the inverse relationship between catalytic activity and selectivity in acetylene partial hydrogenation using dynamic metal–polymer interaction

The partial hydrogenation of acetylene impurities in ethylene is industrially important because acetylene acts as a catalyst poison in downstream ethylene polymerization processes. In this reaction, simultaneously achieving high acetylene conversion and partial hydrogenation selectivity is challenging, and most known catalyst systems exhibit an inverse activity–selectivity relationship. Here, an amorphous polyphenylene sulfide (Am-PPS) was synthesized as a promoter for 0.1 wt% Pd/α-Al2O3. The catalyst modification using a trace amount of Am-PPS (0.15 wt%) enabled a remarkable enhancement of ethylene selectivity without an appreciable loss in acetylene hydrogenation activity. This could be attributed to the dynamic change of the Am-PPS–Pd interface, which selectively allows the cooperative adsorption of acetylene and H2, but not ethylene. Besides, the modified catalyst exhibited excellent long-term stability because of the high thermochemical stability of the polymer. These results demonstrate the unique possibility of using dynamic metal–polymer interaction to design partial hydrogenation catalysts that simultaneously exhibit high activity, selectivity, and stability.

Iodide-Coordinated Single-Site Pd Catalysts for Alkyne Dialkoxycarbonylation

Heterogeneous single-metal-site catalysts (HSMSCs) have attracted considerable interest, but most studies have focused on the metal atoms in the active site while ignoring the key role of ligands. The unique coordination environment of a single-site catalyst is crucial for realizing its potential. Constructing this kind of catalyst via a feasible and practical fabrication method is challenging. Herein, a single-site Pd catalyst with iodide ligands supported on activated carbon (Pd1/AC) was successfully fabricated by atomic dispersion of large Pd nanoparticles (NPs). Intermediate I• radicals were detected during the atomic dispersion process of Pd NPs by in situ imaging photoelectron photoion coincidence spectroscopy (in situ iPEPICO) with vacuum ultraviolet synchrotron radiation. The molecular structure of single-site Pd was established as [Pd(CO)I4(O═AC)]2– through combined characterization. Alkyne dialkoxycarbonylation with high selectivity toward 1,4-dicarboxylic acid esters (>94%) and high acetylene conversion (>99%) was achieved. A sulfonic promoter on the Pd1/AC catalyst for alkyne dialkoxycarbonylation was avoided because of the iodide ligand. Good durability and a broad substrate scope were successfully achieved.

Atomically Dispersed Pd Atoms on a Simple MgO Support with an Ultralow Loading for Selective Hydrogenation of Acetylene to Ethylene.

We report a simple and efficient Pd/MgO catalyst loaded with ppm level of Pd (7.8 ppm) for semi-hydrogenation of acetylene to ethylene. The catalyst showed excellent performance with high acetylene conversion (97%), high ethylene selectivity (89%) and good stability. Moreover, the atomically dispersed Pd atoms are inactive for ethylene hydrogenation. Isotopic and FTIR results suggest that H2 dissociates at isolated Pd atoms in a heterolytic manner forming O-H bond, which may account for the high selectivity.

CATALYTIC SYNTHESIS OF A LINE BY ACETYLENE HYDRATION

Acetone is a valuable chemical product. It can be obtained by oxidative dehydrogenation of isopropyl alcohol, oxidation of propylene, decomposition of acetic acid and ethyl alcohol, oxidation of cymene and others. Among the known processes for the production of acetone, the most promising is the synthesis by hydration of acetylene in the presence of catalysts. The advantage of this method is the possibility of carrying out the process in existing plants for the production of acetic aldehyde. On the other hand, the process of simultaneously producing acetaldehyde and acetone under the influence of multifunctional catalysts and carrying out the process using flexible technology is promising. The vapor-phase hydration of acetylene with the formation of acetone on polyfunctional catalysts was studied. Process parameters are found that provide acetone with high selectivity and acetylene conversion. At present, acetic aldehyde is mainly obtained by two methods - hydration of acetylene and oxidation of ethylene. The process of hydration of acetylene to acetic aldehyde in the presence of catalysts has been studied quite well. Numerous catalysts have been proposed for this process. Among the known catalysts for hydration of acetylene to acetic aldehyde, the most active was the cadmium calcium phosphate catalyst (CCF), which is recommended for industrial use. However, cadmium calcium phosphate catalyst is not without drawbacks. The average yield of acetaldehyde in one pass of acetylene does not exceed 7.0%. The CCF catalyst is very sensitive to temperature changes, its service life before regeneration does not exceed 72-76 hours. Keywords: acetone, propylene, hydration process, catalyst, crosslinking, multifunctional properties.

Gas–solid acetylene dimerization over copper-based catalysts

A gas–solid acetylene dimerization over copper-based catalysts, with high acetylene conversion and MVA selectivity and convenient operation, was reported.

Metal–organic framework‐derived cobalt and nitrogen co‐doped porous carbon with four‐coordinated Co–Nx for efficient acetylene hydrochlorination

Industrial production of vinyl chloride through acetylene hydrochlorination is a dominating technique in coal‐rich areas, but its development is severely restricted by the use of toxic mercury chloride (HgCl2) catalyst. Inspired by the fact that doped carbon materials active in acetylene hydrochlorination often have good performance in the oxygen reduction reaction, a series of cobalt and nitrogen co‐doped porous carbon catalysts prepared by pyrolysis of bimetallic ZIFs based on ZIF‐8 and ZIF‐67 under N2 were applied in acetylene hydrochlorination. The catalytic activities of the co‐doped catalysts varied with Co addition, and the highest acetylene conversion could be up to 83% with a space velocity of 2.6 ml g−1 min−1 at 220°C when a small amount of cobalt was introduced. Results of several characterizations confirmed the existence of Co–Nx in the co‐doped carbons, pointing out that this coordination structure makes the catalysts have better ability to adsorb and activate C2H2. Density functional theory calculation finally proved that C atom adjacent to the N atom in Co–N4 structure is the primary active site in co‐doped catalysts with high activity. We also conclude that the decreased N content caused by Co2N decomposition and the coordination structure change of Co–Nx should be responsible for the gradually worsening performances of the carbon catalysts with further Co addition. Our study provides a new route for improving the performance of N‐doped carbon material in acetylene hydrochlorination and thus enhances its potential for practical application.

Activation of the Highly‐Selective Pd11Bi2Se2 during the Semi‐Hydrogenation of Acetylene

Pd11Bi2Se2 was prepared as single‐phase material and used in an unsupported state as catalyst in the semi‐hydrogenation of acetylene in ethylene excess. After an initial inactive time‐period, Pd11Bi2Se2 activated and showed high acetylene conversion and selectivity towards ethylene at 473 K. In addition, after the initial inactive state, the compound revealed high stability during 100 h time on stream. At 80 % conversion the selectivity to ethylene is higher than 90 %. Post‐catalysis investigations by powder X‐ray diffraction (p‐XRD) and X‐ray photoelectron spectroscopy (XPS) exclude the formation of intermetallic hydrides, decomposition, and the presence of elemental palladium. Furthermore, comparison of XPS before and after catalysis revealed the reason of the inactive state of the intermetallic compound during the first hours of catalysis. An initial surface layer of bismuth oxide is reduced and re‐incorporated into the intermetallic compound. This material change is responsible for the initially observed activation of Pd11Bi2Se2 during the semi‐hydrogenation of acetylene.

Selective hydrogenation of acetylene on SiO2 supported Ni-In bimetallic catalysts: Promotional effect of In

Ni/SiO2 and the bimetallic NixIn/SiO2 catalysts with different Ni/In ratios were tested for the selective hydrogenation of acetylene, and their physicochemical properties before and after the reaction were characterized by means of N2-sorption, H2-TPR, XRD, TEM, XPS, H2 chemisorption, C2H4-TPD, NH3-TPD, FT-IR of adsorbed pyridine, and TG/DTA and Raman. A promotional effect of In on the performance of Ni/SiO2 was found, and NixIn/SiO2 with a suitable Ni/In ratio gave much higher acetylene conversion, ethylene selectivity and catalyst stability than Ni/SiO2. This is ascribed to the geometrical isolation of the reactive Ni atoms with the inert In ones and the charge transfer from the In atoms to Ni ones, both of which are favorable for reducing the adsorption strength of ethylene and restraining the CC hydrogenolysis and the polymerizations of acetylene and the intermediate compounds. On the whole, Ni6In/SiO2 and Ni10In/SiO2 had better performance. Nevertheless, with increasing the In content, the selectivity to the C4+ hydrocarbons tended to increase due to the enhanced catalyst acidity because of the charge transfer from the In atoms to Ni ones. As the Lewis acid ones, the In sites could promote the polymerization. The catalyst deactivation was also analyzed. We propose that the Ni/SiO2 deactivation is mainly attributed to the phase change from metallic Ni to nickel carbide. The introduction of In inhibited the formation of nickel carbide. However, as the In content increased, the carbonaceous deposit became the main reason for the NixIn/SiO2 deactivation due to the enhanced catalyst acidity.

Silicate fiberglass catalysts: From science to technology

Efficient methods for the confining of highly dispersed Pd and Pt particles 1–1.5 nm in size in the subsurface layers of silicate glass fibers at depths of 10–20 nm are developed. Fiberglass catalysts reveal high activity in the selective hydrogenation of acetylene and the deep oxidation of hydrocarbons despite their low metal contents (0.01–0.02 wt %). The monometallic Pd/FG catalyst thus exhibits higher C2H2 hydrogenation selectivity at high acetylene conversion (99%+) in comparison to the commercial bimetallic Pd–Ag catalyst, and the activity of the Pt/FG catalyst in the deep oxidation of organic and chlororganic compounds, including dioxins, is found to be higher than that of the commercial AP-56 (Pt/Al2O3) catalyst. The efficiency of Pt/FG has successfully been demonstrated in the removal volatile organic compounds (VOC) from Monomer plant of PJSC Nizhnekamskneftekhim for more than four years of continuous operation.

Hydrochlorination of acetylene using expanded multilayered vermiculite (EML-VMT)-supported catalysts

Abstract Catalyst supports have very important effects on catalyst performance. A novel expanded multilayered vermiculite (EML-VMT) is successfully used as the catalyst support for the acetylene hydrochlorination. By mixing carbon on the surface of EML-VMT ( i.e. , EML-VMT-C), the HgCl 2 /EML-VMT-C achieved a high acetylene conversion of 97.3%, a vinyl chloride selectivity of 100% and a turn over frequency (TOF) value of 8.83 × 10 −3 s −1 at a temperature of 140 °C, an acetylene gas hourly space velocity (GHSV) of 108 h −1 , and a feed volume ratio V(HCl)/V(C 2 H 2 ) of 1.15. Moreover, the HgCl 2 /EML-VMT-C shows good stability. The EML-VMT also shows potential in the preparation of other EML-VMT-supported catalysts.

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.

Radio-frequency H2 plasma treatment of AuPd/TiO2 catalyst for selective hydrogenation of acetylene in excess ethylene

Supported Au catalysts modified by addition of small amount of Pd (Au/Pd atomic ratio=14) are prepared by deposition-precipitation with NH3 (DP-NH3) followed by impregnation methods on TiO2. Low-pressure radio-frequency (RF) H2 plasma treatment has been applied to AuPd/TiO2 for the selective hydrogenation of acetylene. Compared with conventional thermal reduction (AuPd-250), the acetylene conversion over plasma-treated catalyst (AuPd-P) has been improved significantly while the ethylene selectivity shows the opposite trend. With additional thermal reduction on the plasma-treated catalyst (AuPd-P250), the acetylene conversion is decreased and the ethylene selectivity is increased, however, they are still in between those of AuPd-P and AuPd-250. To understand the plasma effect, the catalysts are characterized by XPS, in situ FTIR spectra of CO adsorption and pulse H2 chemisorption techniques. The high acetylene conversion of AuPd-P is ascribed to its large amount of surface Pd sites for acetylene adsorption, while its poor ethylene selectivity is due to the formation of contiguous Pd ensembles, which will cause the over hydrogenation of acetylene. The DTG results of the used catalyst indicate that the formation of green oil on or in the vicinity of Pd is suppressed over AuPd-P and AuPd-P250, and that is the reason why the plasma-treated samples are less deactivated than AuPd-250.

Hydrochlorination of Acetylene Using SiC Foam Supported Structured C/Au Catalysts

AuCl3 loaded structured catalysts were prepared on SiC foam supported with pre-coated activated carbon layers. The catalytic properties of the structured catalysts towards hydrochlorination of acetylene were tested in a fixed-bed reactor with the AuCl3 loaded on activated carbon pellets as a reference. For isopyknic catalysts, the structured catalyst with only one fifth of the Au amount as that was used on the reference catalyst exhibited even a little higher acetylene conversion and much better stability than the latter no matter what the gas hourly space velocities of acetylene were used. The results indicated that the more homogeneous distribution of AuCl3 particles and better heat transfer along the fixed-bed reactor originated from the low pressure drop and high thermal conductivity of the SiC foam supported structured catalysts might be able to account for their improved efficiency and stability. It is believed that these novel structured C/Au catalysts can be potentially applied in VCM industrialization in view of their greatly reduced cost and much prolonged life.

Stability improvement of the Nieuwland catalyst in the dimerization of acetylene to monovinylacetylene

In the process of dimerization of acetylene to produce monovinylacetylene (MVA), the loss of active component CuCl in the Nieuwland catalyst due to the formation of a dark red precipitate was investigated. The formula of the precipitate was CuCl·2C2H2·1/5NH3, and it was presumed to be formed by the combination of NH3, C2H2 and [Cu]-acetylene p-complex, which was an intermediate in the dimerization reaction. The addition of hydrochloric acid into the catalyst can reduce the formation of precipitate, whereas excessive H+ is unfavorable to the dimerization reaction of acetylene. To balance between high acetylene conversion and low loss rate of CuCl, the optimum mass percentage of HCl in the added hydrochloric acid was determined. The result showed the optimum mass percentage of HCl decreased from 5.0% to 3.2% when the space velocity of acetylene was from 140 h−1 to 360 h−1. The result in this work also indicated the pH of the Nieuwland catalyst should be kept in the range of 5.80–5.97 during the reaction process, which was good for both catalyst life and acetylene conversion.

Selective hydrogenation of acetylene in ethylene rich feed streams at high pressure over ligand modified Pd/TiO2

The selective hydrogenation of acetylene from ethylene rich streams was conducted at high pressure and in the presence of CO over two 1 wt% loaded Pd/TiO2 catalysts with differing dispersions. Although, the more poorly dispersed sample did not result in high acetylene conversion only a small proportion of the total available ethylene was hydrogenated to ethane. The more highly dispersed sample was able to remove acetylene to a level below the detection limit but this was at the expense of significant proportion (ca. 30%) of the available ethylene. Modification of the catalysts by exposure to triphenyl phosphine or diphenyl sulfide and subsequent reduction at 393 K led to improved performance with increased conversion of acetylene and decreased propensity to hydrogenate ethylene resulting in an overall net gain in ethylene. The higher dispersed sample which had been ligand modified provided the best results overall and in particular for the diphenyl sulfide treated sample which was able to completely eliminate acetylene and still obtain a net gain in ethylene. The differences observed are thought to be due to the creation of appropriate active ensembles of Pd atoms which are able to accommodate acetylene but have limited ability to adsorb ethylene. Sub-surface hydrogen formation was suppressed, but not eliminated, by exposure to modifier.

An Efficient Catalyst for the Large Scale Production of Multi-Walled Carbon Nanotubes

The main objective of this work is to design an efficient catalyst for the synthesis of multiwalled carbon nanotubes (MWNTs) in our scalable, high quality with gram amount synthesis. The catalysts with composition of Fe, Mo, and MgO in the molar ratios 1:0.5:13, 1:1:13, and 1:1:50 were prepared by combustion method. The high acetylene conversion and carbon yield of chemical vapor deposition (CVD) reaction suggest the formation of MWNTs by 1:1:50 molar ratio catalysts under pyrolysis of the pure C2H2 gas with the flow rate about 60 mL/min at 800 C for 30 min. The catalysts and the resulting CNT samples were analyzed by XRD, TGA, FT-Raman, SEM, and TEM to establish a relation between catalyst design and MWNT yield. Raman results indicate that CNTs are in multiwalled structure, since no single-walled characteristic features appear in the 200–400 cm–1 region. We give evidence that increased carbon conversion, carbon yields and % purity of more than 65%, 1000%, and 99%, respectively, with respect to our catal...

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.