Homogeneous-like Alkyne Selective Hydrogenation Catalyzed by Cationic Nickel Confined in Zeolite

Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes

Selective hydrogenation of alkynes to alkenes remains challenging in the field of catalysis due to the ease of over-hydrogenated of alkynes to alkanes. Favorably, the incorporation of metal nanopar...

The effects of both carbon monoxide (as a gas phase additive) and potassium (as a catalyst additive) on the selective hydrogenation of acetylene over Pd/Al$\sb2$O$\sb3$ was studied by deuterium tracer experiments combined with Kemball's steady-state treatment and temperature programmed reaction (TPR). The TPR of acetylene and ethylene in hydrogen, which was attempted in this study for the first time, enabled the investigation of the behavior of the adsorbed species on Pd. CO addition to the reaction mixture significantly increased the probability of ethylene desorption during ethylene deuteration while minor effects due to CO displacement of hydrogen were observed for acetylene deuteration. In the case of selective removal of trace acetylene from ethylene streams, results suggest that CO blockage of H$\sb2$ adsorption sites is less important than CO displacement of ethylene in improving the overall selectivity of the industrial process. In acetylene TPR, preadsorbed CO induced changes in oligomer yields, delayed desorption of oligomers and suppressed self-hydrogenation during the adsorption of acetylene. These results indicate that CO blocks the adsorption sites which accommodate acetylene and the hydrogen product from acetylene dissociation to result in the suppression of initiation and propagation reactions for oligomers. Potassium doped catalysts yielded an enhancement in actylene hydrogenation selectivity to ethylene, an increase in the rate of the acetylene hydrogenation reaction, and an increase in the oligomer yield from the hydrogenation of acetylene. In the acetylene TPR spectra of K doped catalysts, shifts of oligomer peaks to lower temperatures were observed, indicating the desorption of the adsorbed species was enhanced by K addition. An increase in the probability of ethylene desorption was also found via ethylene deuteration experiments. A decrease in the rate of ethylene deuteration with K addition was observed, which contrasts with the inhanced rate of acetylene hydrogenation. The observed increase in the acetylene hydrogenation selectivity to ethylene appears to be due to easier ethylene desorption and suppressed ethylene adsorption. All of these effects may be explained by K-induced reduction in hydrocarbon adsorption strength. The effect of K arises through metal-support interactions.

Ligand screening for palladium nanocatalysts towards selective hydrogenation of alkynes

Selective Hydrogenation of Acetylene over a MoP Catalyst

In this research, a heterogeneous Nano-Structured functionalized SBA-15 metformin palladium composite catalyst is reported for the selective hydrogenation of alkynes. In the first place, A series of the heterogeneous mesoporous SBA-15 metformin palladium catalyst were prepared and afterwards the condition and the ratio of used materials were optimized to give rise a suitable high performance catalyst. The final nano-structured catalyst was characterized by X-ray powder diffraction, BET surface area, FT-IR spectrophotometer, Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) and served in partial hydrogenation of different alkynes, with high selectivity and high yield. The liquid phase hydrogenation was conducted under mild condition of room temperature and atmospheric pressure. The reactions were monitored every half an hour by gas chromatography and all of them were completed during 4-6 hours. The products were characterized by 1H-NMR, 13C-NMR, FT-IR, and Mass Spectrometry (MS) that strongly confirmed the (Z)-double bond configuration of produced alkenes. This prepared catalyst is competitive with the best palladium catalysts known for the selective liquid phase hydrogenation of alkynes and can be easily recovered and regenerated with keeping high activity and selectivity over multiple cycles with a simple regeneration procedure.

Efficient selective hydrogenation of terminal alkynes over Pd–Ni nanoclusters encapsulated inside S-1 zeolite

Reduced Foulant Formation During the Selective Hydrogenation of C2, C3, and C4 Acetylenes

The selective hydrogenation of acetylene catalyzed by Pd nanoparticles is industrially used to increase the purity of ethylene. Despite the implementation of Pd based catalysts on an industrial scale, little is known about metal-support interactions on a fundamental level due to the complexity of these systems. In this study, the influence of metal-support interactions between Pd nanoparticles and two electronically modified a-SiO2 thin films on acetylene hydrogenation is investigated under ultra-high vacuum (UHV) conditions. The hydrogenation is performed under isothermal reaction conditions using a pulsed molecular beam reactive scattering (pMBRS) technique. Besides the activity and selectivity of clean Pd particles also the impact of dehydrogenated species intentionally introduced a priori is elucidated, whereas the active phase of the catalyst is additionally characterized by CO infrared reflection-absorption spectroscopy (IRRAS) and post-mortem temperature-programmed reaction (TPR). Metal-support interactions are found to influence the catalytic properties of Pd particles by charge-transfer, where positive charging leads to increased activity for acetylene hydrogenation. However, the increased activity is accompanied by formation of undesired byproducts. The active sites for acetylene and ethylene hydrogenation are shown to be different as previously proposed by the A and E model. The availability of the two different active sites on the Pd nanoparticles is determined by dehydrogenated species, whose nature and stability can be tuned by metal-support interactions. Based on these findings an electronic model is proposed how selectivity for acetylene hydrogenation can be steered solely by metal-support interactions leading to blocking of unselective sites in situ.

Boosting the activity of PdAg2/Al2O3 supported catalysts towards the selective acetylene hydrogenation by means of CO-induced segregation: A combined NAP XPS and mass-spectrometry study

Selective hydrogenation of acetylene in the presence of ethylene on K+-β-zeolite supported Pd and PdAg catalysts

Selective acetylene hydrogenation is a crucial reaction for purifying ethylene in the petroleum industry and presents a promising non-oil route for producing ethylene by integrating acetylene production from natural gas and coal. Despite significant advancements in catalyst development, achieving both high catalytic activity and ethylene selectivity remains challenging due to competing side reactions, including over-hydrogenation to ethane, C-C coupling leading to oligomers, and C-C bond cleavage resulting in coke formation. This review provides a comprehensive overview of recent progress in the development of catalysts and understanding of reaction mechanism for acetylene hydrogenation to ethylene. Firstly, benchmarks for conversion and selectivity calculation are critically discussed. Then, research on active site design is categorized into monometallic sites, disordered alloy sites, intermetallic compound (IMC) sites, and single-atom (SA) sites, with a distinction between Pd-based and non-Pd-based catalysts. This categorization highlights the active site design strategies and summarizes state-of-the-art performance metrics. Emphasis is placed on the structure-performance relationships and the role of different active metals in enhancing ethylene selectivity and catalytic activity. In addition, the roles of catalyst support and modifiers are reviewed. Finally, we discuss challenges and future research directions in mechanistic understanding and catalyst design, aiming to guide further innovations in this important field.

Synergistic and size effects in selective hydrogenation of alkynes on gold nanocomposites

The Selective Hydrogenation of Acetylene by the Electrochemically Pumped Hydrogen Over Cu in the Presence of Abundant Ethylene

Carbonaceous species, including subsurface carbidic carbon and surface carbon, play crucial roles in heterogeneous catalysis. Many reports suggested the importance of subsurface carbon in the selective hydrogenation of alkynes over Pd‐based catalysts. However, the role of surface carbon has been largely overlooked. We demonstrate that subsurface carbon in Pd is not responsible for the selectivity in acetylene hydrogenation. In contrast, the structure of surface carbonaceous species plays a decisive role in hydrogenation selectivity. Electron microscopy and spectroscopy evidence, along with theoretical modelling, reveal that partial graphitization of surface carbonaceous species results in unique spatial confinement of surface reaction intermediates, thus altering the reaction energy landscape in favour of ethylene desorption as opposed to over‐hydrogenation. This mechanism for selectivity control is analogous to enzyme catalysis, where the active centers selectively attract reactants and release products. Similar mechanism may be present in CO/CO2 hydrogenation and alkane dehydrogenation reactions.