Acetylene In Excess Ethylene Research Articles

Functionalized ionic liquid coatings in the Pd-catalyzed selective hydrogenation of acetylene in ethylene-rich feeds

This study explores the tuning of a Pd/Al2O3 hydrogenation catalyst for the selective removal of trace acetylene from ethylene-rich feeds by coating the catalyst with non-functionalized and functionalized ionic liquids (denoted as SCILL and Advanced SCILL materials, respectively). These materials were tested in an automated continuous hydrogenation rig converting 3300 ppm of acetylene in excess ethylene, a gas mixture mimicking a technical front-end steam cracker feed composition. While the sulfonic-acid-functionalized IL coating resulted in a highly active but very unselective catalyst converting mainly ethylene to ethane, an Advanced SCILL catalyst prepared from a nitrile-functionalized IL reduced the acetylene concentration down to less than 1 ppm, while leaving over 99% of the ethylene untouched. We also examined the potential transformations of the IL layer under reaction conditions by means of 1H NMR. Except for a ketone-functionalized IL, which was inherently labile, all tested ILs primarily underwent C2-ethylation or remained unaltered. Our findings highlight the great potential of functionalized ILs in modifying heterogeneous hydrogenation catalysts.

Hydrophobic Surface Modification of Cu-Based Catalysts for Enhanced Semihydrogenation of Acetylene in Excess Ethylene

Hydrophobic Surface Modification of Cu-Based Catalysts for Enhanced Semihydrogenation of Acetylene in Excess Ethylene

Photo-thermo semi-hydrogenation of acetylene on Pd1/TiO2 single-atom catalyst

Semi-hydrogenation of acetylene in excess ethylene is a key industrial process for ethylene purification. Supported Pd catalysts have attracted most attention due to their superior intrinsic activity but often suffer from low selectivity. Pd single-atom catalysts (SACs) are promising to significantly improve the selectivity, but the activity needs to be improved and the feasible preparation of Pd SACs remains a grand challenge. Here, we report a simple strategy to construct Pd1/TiO2 SACs by selectively encapsulating the co-existed small amount of Pd nanoclusters/nanoparticles based on their different strong metal-support interaction (SMSI) occurrence conditions. In addition, photo-thermo catalysis has been applied to this process where a much-improved catalytic activity was obtained. Detailed characterization combined with DFT calculation suggests that photo-induced electrons transferred from TiO2 to the adjacent Pd atoms facilitate the activation of acetylene. This work offers an opportunity to develop highly stable Pd SACs for efficient catalytic semi-hydrogenation process.

Synergizing metal-support interactions and spatial confinement boosts dynamics of atomic nickel for hydrogenations.

Atomically dispersed metal catalysts maximize atom efficiency and display unique catalytic properties compared with regular metal nanoparticles. However, achieving high reactivity while preserving high stability at appreciable loadings remains challenging. Here we solve the challenge by synergizing metal-support interactions and spatial confinement, which enables the fabrication of highly loaded atomic nickel (3.1 wt%) along with dense atomic copper grippers (8.1 wt%) on a graphitic carbon nitride support. For the semi-hydrogenation of acetylene in excess ethylene, the fabricated catalyst shows extraordinary catalytic performance in terms of activity, selectivity and stability-far superior to supported atomic nickel alone in the absence of a synergizing effect. Comprehensive characterization and theoretical calculations reveal that the active nickel site confined in two stable hydroxylated copper grippers dynamically changes by breaking the interfacial nickel-support bonds on reactant adsorption and making these bonds on product desorption. Such a dynamic effect confers high catalytic performance, providing an avenue to rationally design efficient, stable and highly loaded, yet atomically dispersed, catalysts.

Highly Selective Acetylene Semihydrogenation Catalyst with an Operation Window Exceeding 150 °C

The operating window (OW) is a primary performance criterion for the selective hydrogenation of acetylene in excess ethylene. Currently, most state-of-the-art catalyst systems have an OW of less th...

High Performance of Single‐atom Catalyst Pd1/MgO for Semi‐hydrogenation of Acetylene to Ethylene in Excess Ethylene

AbstractSemi‐hydrogenation of acetylene in excess ethylene is important in purifying alkene streams. Industrially used Pd‐based catalysts are highly active but suffer from low selectivity. Supported Pd single‐atom catalysts (SACs) are promising in this reaction but the fabrication of highly stable Pd SACs remains a grand challenge. In this work, we have developed a stable MgO supported Pd SAC by ball‐milling method which showed good catalytic performance. The strong interaction between Pd atoms and MgO support not only inhibited the aggregation of Pd atoms, but also resulted in a high chemical state of Pd which may facilitate the adsorption as well as reactivity of acetylene. In addition, the isolation nature of the SAC is in favour of ethylene desorption, giving rise to a high selectivity. This work provided a good example to develop highly stable Pd SAC for catalytic semi‐hydrogenation reaction with high efficiency.

Preparation of an Unsupported Copper-Based Catalyst for Selective Hydrogenation of Acetylene from Cu2O Nanocubes

Designing cheap, earth-abundant, and nontoxic metal catalysts for acetylene hydrogenation is of pivotal importance, but challenging. Here, a nonprecious metal catalyst for selective hydrogenation of acetylene in excess ethylene was prepared from Cu2O nanocubes. The preparation includes two steps: (1) thermal treatment in acetylene-containing gas at 160 °C and (2) hydrogen reduction at 180 °C. The resultant catalyst showed outstanding performance at low temperature (80-100 °C) and 0.1-0.5 MPa pressure, completely converting acetylene with a low selectivity to undesired ethane (<20%). The characterization results of high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy corroborated that the formation of an interstitial copper carbide (CuxC) might give rise to significantly enhanced hydrogenation activity. Preliminary density functional theory calculation demonstrated that the lattice spacing of Cu3C was nearly identical to that of the new CuxC crystallite measured in HRTEM and determined by XRD. The calculated dissociation energy of hydrogen on Cu3C(0001) was considerably lower than that on Cu(111), suggesting superior hydrogenation activity of Cu3C(0001). It is experimentally verified that copper(I) acetylide (Cu2C2) might be the precursor of CuxC. Cu2C2 underwent partial hydrogenation to fabricate CuxC crystallites and the thermal decomposition to Cu and carbon materials in parallel.

PdIn/Al2O3 Intermetallic Catalyst: Structure and Catalytic Characteristics in Selective Hydrogenation of Acetylene

The structure and catalytic characteristics of a bimetallic catalyst containing Pd1In1 nanoparticles deposited on the surface of γ-Al2O3 were studied. The formation of intermetallic nanoparticles was determined by X-ray diffraction analysis and confirmed by X-ray photoelectron spectroscopy and IR spectroscopy of adsorbed CO. In the hydrogenation of acetylene in excess ethylene, PdIn/Al2O3 had significantly higher selectivity of ethylene formation (~86%) than monometallic Pd/Al2O3 (~35%). The high selectivity of PdIn/Al2O3 is explained by two factors: (1) the formation of monatomic Pd1 sites isolated from one another by In atoms and (2) the change in the electronic state of Pd atoms in the intermetallic nanoparticles.

Selective hydrogenation of acetylene over Pd on glass fiber catalysts

Key properties of silicate glasses are highlighted including the capability of stabilizing disperse Pd nanoparticles in the bulk of glass fibers (GF), high solubility of acetylene and hydrogen, as well as their high mobility. These properties provide the high activity and selectivity of Pd/GF catalysts to hydrogenation of acetylene in excess ethylene over a wide range of acetylene conversions up to its complete one. For a wide variety of mono-, bimetallic systems including catalysts with single palladium atoms, TOF was established to depend only slightly on the palladium dispersion and support nature, i.e. the reaction can be considered structure-insensitive. Nevertheless, a TOF decrease was observed in the systems with single atoms; that was accounted for by declining of the hydrogen dissociation rate or its slower spillover. Isotope-kinetic data were used for determining quantitatively undesirable contributions to the process selectivity caused by both hydrogenation of acetylene and gas-phase ethylene to ethane. High selectivities of alloyed bimetallic systems comprising isolated palladium atoms at approaching to the complete conversion of acetylene were caused by the low rate of hydrogenation of weakly adsorbed ethylene to ethane while for Pd/GF catalysts by the complete exclusion of the hydrogenation of ethylene from gas-phase.

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.

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

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.

In Situ Spectroscopic Characterization of Ni1–xZnx/ZnO Catalysts and Their Selectivity for Acetylene Semihydrogenation in Excess Ethylene

The structures of ZnO-supported Ni catalysts were explored with in situ X-ray absorption spectroscopy, temperature-programmed reduction, X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy, and electron energy loss spectroscopy. Calcination of nickel nitrate on a nanoparticulate ZnO support at 450 °C results in the formation of Zn-doped NiO (ca. Ni0.85Zn0.15O) nanoparticles with the rock salt crystal structure. Subsequent in situ reduction monitored by X-ray absorption near-edge structure (XANES) at the Ni K edge reveals a direct transformation of the Zn-doped NiO nanoparticles to a face-centered cubic alloy, Ni1–xZnx, at ∼400 °C with x increasing with increasing temperature. Both in situ XANES and ex situ HRTEM provide evidence for intermetallic β1-NiZn formation at ∼550 °C. In comparison to a Ni/SiO2 catalyst, Ni/ZnO necessitates a higher temperature for the reduction of NiII to Ni0, which highlights the strong interaction between Ni and the ZnO support. The catalytic activity for acetylene removal from an ethylene feed stream is decreased by a factor of 20 on Ni/ZnO in comparison to Ni/SiO2. The decrease in catalytic activity of Ni/ZnO is accompanied by a reduced absolute selectivity to ethylene. H–D exchange measurements demonstrate a reduced ability of Ni/ZnO to dissociate hydrogen in comparison to Ni/SiO2. These results of the catalytic experiments suggest that the catalytic properties are controlled, in part, by the zinc oxide support and stress the importance of reporting absolute ethylene selectivity for the catalytic semihydrogenation of acetylene in excess ethylene.

Pd–Ag/SiO2 bimetallic catalysts prepared by galvanic displacement for selective hydrogenation of acetylene in excess ethylene

A series of bimetallic Pd–Ag/SiO2 catalysts with Ag enriched on the surface were prepared by galvanic displacement. The bimetallic effect for these catalysts on acetylene hydrogenation was discussed.

Improved selectivity of carbon-supported palladium catalysts for the hydrogenation of acetylene in excess ethylene

In this study we examine the role of the support for selective hydrogenation of acetylene. Palladium (Pd) nanoparticles with a narrow size distribution were deposited on three supports, carbon, alumina and magnesia. The Pd particles ranged from 0.5 to 1.0nm in diameter. A novel synthesis based on room temperature alcohol reduction of the Pd acetate precursor allowed us to deposit similar sized Pd particles on all three supports. We used electron microscopy and X-ray absorption spectroscopy (EXAFS) to characterize these samples and to confirm the similarity of the distribution and the size of the nanoparticles on all three supports. The carbon-supported Pd yielded a higher selectivity to ethylene at 100% acetylene conversions (from acetylene/ethylene mixtures) when compared to the oxide-supported samples. This work provides clear evidence that the support can play an important role in the selective hydrogenation of acetylene. While alumina is extensively used in industry as the support for Pd and Pd alloys, considerable improvements in selectivity could be made by the use of carbon supports.

Promotional effect of Pd single atoms on Au nanoparticles supported on silica for the selective hydrogenation of acetylene in excess ethylene

A Pd single-atom alloy (SAA) structure was constructed by alloying Pd with Au supported on silica. The XRD and HRTEM results demonstrated that the addition of a small amount of Pd efficiently prevented the sintering of Au nanoparticles. The DRIFTS and EXAFS results confirmed that the Pd SAA structure was formed when the atomic ratios of Pd/Au were lower than 0.025. The Pd SAA structure exhibits a much better catalytic performance for the selective hydrogenation of acetylene in excess ethylene than the corresponding monometallic Au or Pd systems.

Selective hydrogenation of acetylene in excess ethylene using Ag- and Au–Pd/SiO2 bimetallic catalysts prepared by electroless deposition

Selective hydrogenation of acetylene in excess ethylene has been investigated for a series of Ag- and Au–Pd/SiO2 bimetallic catalysts having incremental surface coverages of Ag and Au on the Pd surface. The catalysts were prepared by electroless deposition and characterized by atomic absorption spectroscopy and selective chemisorption. Both Ag- and Au–Pd/SiO2 catalysts showed increased selectivity of acetylene conversion to form ethylene, rather than ethane, at high coverages. The catalyst performance results suggest that at high coverages of Ag or Au on Pd, that result in small ensembles of Pd sites, acetylene is adsorbed as a π-bonded species that favors hydrogenation to ethylene. At low coverages, where ensemble sizes of contiguous Pd surface sites are much larger, acetylene is strongly adsorbed as a multi-σ-bonded species which preferentially forms ethane, lowering the selectivity to ethylene. Both kinetic analyses and the calculated turnover frequencies of acetylene conversion and ethane formation were consistent with the above explanation. The similar performance trends for Ag- and Au–Pd/SiO2 suggest that the bimetallic effect for these catalysts is geometric and not electronic in nature.

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.

Selective hydrogenation of acetylene in excess ethylene over SiO2 supported Au–Ag bimetallic catalyst

Supported gold nanocatalysts have been reported to be active in selective hydrogenation of acetylene. In this work, SiO2 supported Au–Ag bimetallic catalyst is studied in the selective hydrogenation of acetylene in excess ethylene. Au and Ag were reductively deposited on a silica surface functionalized by APTES (3-aminopropyltriethoxysilane). They form Au–Ag alloy nanoparticles of very small size. The catalytic activity of Au–Ag bimetallic system showed better catalytic activity at high temperature than that of monometallic gold catalyst. According to the TEM and XRD results, Ag stabilized the nanoparticles against sintering during high temperature calcinations. Non-thermal O2 plasma was applied to remove the APTES under mild conditions instead of high temperature calcination. The results showed that the conversion of acetylene was much higher over Au–Ag/SiO2 catalyst pretreated by O2 plasma than that of pretreated by calcination at 500°C, although the latter catalyst had similar particle size.

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.