Tailoring electronic properties and kinetics behaviors of Pd/N-CNTs catalysts for selective hydrogenation of acetylene

Pd catalyzed selective hydrogenation of acetylene shows remarkable electronic effects. In this work, a strategy is proposed to tailor the electronic properties of Pd nanoparticles by nitrogen doping of carbon nanotubes (CNT) support toward the improved reaction kinetics. While excluding the Pd size effects, the intrinsic promotional effects of the nitrogen doping are demonstrated, which are mainly due to the increased Pd electron density resultant from the presence of more graphitic nitrogen species based on X-ray photoelectron spectroscopy measurements and density functional theory (DFT) calculations. Kinetics analysis and C₂H₂/C₂H₄-temperature-programmed desorption (TPD) measurements reveal that the electron-rich Pd catalyst with the moderately weakened adsorption strength can give rise to the decreased activation energy and thus the simultaneously enhanced activity, selectivity, and stability. The aspects demonstrated here could guide the rational design and optimization of Pd catalysts for the selective hydrogenation of acetylene.     

Catalytic hydrogenation of linoleic acid on nickel,copper, and palladium

The catalytic activity and selectivity for hydrogenation of linoleic acid were studied on Ni, Cu, and Pd catalysts. A detailed analysis of the reaction product was performed by a gas-liquid chromatograph, equipped with a capillary column, and Fourier transform-infrared spectroscopy. Geometrical and positional isomerization of linoleic acid occurred during hydrogenation, and many kinds of linoleic acid isomers (trans-9,trans-12; trans-8,cis-12 orcis-9,trans-13; cis-9,trans-12; trans-9,cis-12 andcis-9,cis-12 18∶2) were contained in the reaction products. The monoenoic acids in the partial hydrogenation products contained eight kinds of isomers and showed different isomer distributions on Ni, Cu, and Pd catalysts, respectively. The positional isomers of monoenoic acid were produced by double-bond migration during hydrogenation. On Ni and Pd catalysts, the yield ofcis-12 andtrans-12 monoenoic acids was larger than that ofcis-9 andtrans-9 monoenoic acids. On the contrary, the yield ofcis-9 andtrans-9 monoenoic acids was larger than that ofcis-12 andtrans-12 monoenoic acids on Cu catalyst. From these results, it is concluded that the double bond closer to the methyl group (Δ12) and that to the carboxyl group (Δ9) show different reactivity for hydrogenation on Ni, Cu, and Pd catalysts. Monoenoic acid formation was more selective on Cu catalyst than on Ni and Pd catalysts.     

Hydrogenation of Nitrobenzene with Supported Transition Metal Catalysts in Supercritical Carbon Dioxide

Transition metal catalysts such as Pd, Pt, Ru, and Rh supported on carbon, silica and alumina have been examined for the hydrogenation of nitrobenzene (NB) in supercritical carbon dioxide (scCO₂) and in ethanol. The order of hydrogenation activity is Pt>Pd>Ru, Rh in scCO₂ and in ethanol. The effectiveness of the support is C>Al₂O₃, SiO₂ for either Pt or Pd in scCO₂. For all the catalysts, higher selectivity to aniline has been obtained in scCO₂ compared with ethanol. Hydrogenation of nitrobenzene catalyzed with Pd/C and Pt/C catalysts was successfully conducted in scCO₂ with a 100% yield to aniline at a lower reaction temperature of 35 °C. The product aniline (organic phase) can be easily separated from the side‐product water (aqueous phase), solvent (scCO₂), and catalyst (solid) by a simple phase separation process. The hydrogenation of NB is a structure‐sensitive reaction in ethanol as well as in scCO₂ except for a few Pt/C catalysts in which the degree of metal dispersion is small (<0.08).     

Competitive Hydrogenation of Alkyl‐Substituted Arenes by Transition‐Metal Nanoparticles: Correlation with the Alkyl‐Steric Effect

The influence of substituents on rate constants of the hydrogenation of monoalkylbenzenes by transition metal nanoparticles or by classical heterogeneous catalysts can be rationalized in terms of the Taft rule. A series of the initial reaction rate constants obtained from various competitive toluene/benzene and toluene/monoalkylbenzene hydrogenation experiments catalyzed by transition‐metal nanoparticles prepared in the presence of imidazolium ionic liquids or surfactants [Ir(0), Rh(0) and Ru(0)] or by classical heterogeneous catalysts (PtO₂, Rh/C, Rh/Al₂O₃, Ru/C, Ru/Al₂O₃ and Pd/C) have been correlated with the Taft equation . Satisfactory correlation coefficients (r) (between 0.96 and 0.99) and positive slopes (ρ) between 0.38 and 0.83 have been obtained. The results clearly show that the reaction constants for the alkyl‐substituents can be expressed by steric factors and are independent of any other non‐steric factors. It is suggested that bulky alkylbenzene substituents, for both transition metal nanoparticles and classical heterogeneous hydrogenation reactions, lower the overall hydrogenation rate, implying a more disturbed transition state compared to the initial state of the hydrogenation (in terms of the Horiuti–Polanyi mechanism). This competitive method is suitable for the estimation of the constant selectivity for couples of alkylbenzenes in which the difference in hydrogenation rates are very high and experimentally difficult to measure and also useful for the design of more selective “nano” and classical catalysts for hydrogenation reactions.     

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.     

Comparison of homogeneous and heterogeneous palladium hydrogenation catalysts

Mechanistic and kinetic studies of Pd-catalyzed hydrogenation at atmospheric pressure and 30–100 C were carried out with methyl sorbate, methyl linoleate and conjugated linoleate. Homogeneous Pd catalysts and particularly Pd-acetylacetonate [Pd(acac)₂] were significantly more selective than Pd/C in the hydrogenation of sorbate to hexanoates, mainlytrans-2-hexenoate. Relative rate constants for the different parallel and consecutive reactions, determined by computer simulation, indicated that the low diene selectivity of Pd/C can be dattributed to a significant direct reduction of sorbate to hexanoate. The similar behavior of PdCl₂ to that of Pd/C suggests that Pd(II) was initially reduced to Pd(O). Valence stabilization of PbCl₂ by adding DMF or a mixture of Ph₃P and SnCl₂ increased the diene selectivity but decreased the activity. Stabilization of Pd(acac)₂ with triethylaluminum (Ziegler catalyst) resulted in increased activity but decreased selectivity. The kinetics of methyl linoleate hydrogenation showed that although Pd(acac)₂ was only half as active as Pd/C, their respective diene selectivity was similar (10.4 and 9.6). The much greater reactivity of conjugated compared with unconjugated linoleate toward Pd(acac)₂ suggests the possible formation of conjugated dienes as intermediates that are rapidly reduced and not detected in the lipid phase during hydrogenation.     

Vapour phase hydrogenation of phenol over Pd/C catalysts: A relationship between dispersion,metal area and hydrogenation activity

A series of palladium supported on activated carbon catalysts, with Pd varying from 0.5 to 6.0 wt%, were prepared via wet impregnation method using PdCl₂ · xH₂O as a precursor salt. The dried samples were further reduced at 573 K in hydrogen and characterized by CO adsorption at room temperature in order to determine the dispersion, metal area and particle size. The catalysts were tested for vapour phase phenol hydrogenation in a fixed-bed all glass micro-reactor at a reaction temperature of 453 K under normal atmospheric pressure. The decrease in metal surface area as well as dispersion with corresponding increase in turn-over frequency (TOF) against palladium loadings suggest the unusual inverse relationship that exist between Pd dispersion and phenol hydrogenation activity over Pd/carbon catalysts. The stability of TOF at larger crystallite size indicates that phenol hydrogenation is less sensitive reaction especially beyond 3 wt% of Pd content. It is evident from the results that structural properties of the catalysts strongly influence the availability of Pd atoms on the surface for CO chemisorption and hence for phenol hydrogenation. A comparison between selectivity and product yield of the reaction against overall phenol conversion indicates that changes in reaction selectivity for cyclohexanone or cyclohexanol is independent of phenol conversion level and either of the product is not formed at the cost of another. The stability of the catalysts with reaction time suggests that coke formation on the surface of the catalyst is less significant and the formation of cyclohexanone remains almost total even at higher reaction temperatures.     

Hydrierung von Crotonaldehyd und Acetaldol mit modifizierten Pd-Trägerkatalysatoren. II. Zum Einfluß einer Chromiummodifizierung auf Pd Al2O3-Katalysatoren

Hydrogenation of Crotonaldehyde and Acetaldol with Modified Pd-Supported Catalysts. II. On the Influence of a Chromium Modification of Pd/Al₂O₃ Catalysts The catalytic properties in hydrogenation reactions on chromium containing Pd/Al₂O₃ catalysts are influenced by an “esemble effect.” The specific activity in the hydrogenation of crotonaldehyde to n-butyraldehyde is independent of the chromium content in the Pd/Al₂O₃ catalysts. But the specific activity for the hydrogenolysis of ethane is decresed with the chromium content of the catalysts. On the other hand, was observed that the specific activity of the conversion of acetaldol to n-butyraldehyde rises with increasing chromium content. This specific activity is higher than the specific hydrogenation activity. This fact can be considered as an argument for an asynchron hydrogenolysis of the hydroxyl group in the formation of n-butyraldehyde from acetaldol on Pd Cr/Al₂O₃ catalysts.     

Silica-supported alloy catalysts for triglyceride hydrogenation: The preparation and properties of Pd–Ag and Pd–Ni systems

The binary metal systems Pd–Ag and Pd–Ni have been prepared on a silica support with a total metal loading of 2.5% (w/w). About a dozen catalysts were prepared in each series covering the range 0–100 at. % Pd. The catalysts were characterised by a number of techniques, principally temperature programmed reduction, differential scanning calorimetry and metal surface area measurement. The catalyst activity and selectivity were measured for the hydrogenation of soya bean oil in both stirred and shaken batch reactors at 1 atm H₂ pressure in the temperature range 100–160°C. The characterisation techniques provided strong evidence of alloying for both series of catalysts. The activity and selectivity measurements also provided supporting evidence of alloying, and the Pd–Ag system exhibited an activity maximum in the 90–100 at. % Pd range, while the Pd–Ni system maintained constant activity for alloys containing 0–60 at. % Ni. Trans-acid formation was suppressed by lower reduction temperature, and linolenate removal was improved at lower temperatures. However, it also appears that reaction rates were dominated largely by triglyceride diffusion effects.     

Hydrogenation of Sunflower Oil over M/SiO2 and M/Al2O3 (M = Ni,Pd, Pt,Co, Cu) Catalysts

This work is aimed at evaluating the performance of several catalysts in the partial hydrogenation of sunflower oil. The catalysts are composed of noble (Pd and Pt) and base metals (Ni, Co and Cu), supported on both silica and alumina. The following order can be proposed for the effect of the metal on the hydrogenation activity: Pd > Pt > Ni > Co > Cu. At a target iodine value of 70 (a typical value for oleomargarine), the production of trans isomers is minimum for supported nickel catalysts (25.7–32.4 %, depending on the operating conditions). Regarding the effect of the support, Al₂O₃ allows for more active catalysts based on noble metals (Pd and Pt) and Co, the effect being much more pronounced for Pt. Binary mixtures of catalysts have been studied, in order to strike a balance between catalyst activity and product distribution. The results evidence that Pd/Al₂O₃–Co/SiO₂ mixture has a good balance between activity and selectivity, and leads to a very low production of trans isomers (11.8 %) and a moderate amount of saturated stearic acid (13.5 %). Consequently, the utilization of cobalt‐based catalysts (or the addition of cobalt to other metallic catalysts) could be considered a promising alternative for the hydrogenation of edible oil.     

Characteristics and Catalytic Properties of Mesocellular Foam Silica Supported Pd Nanoparticles in the Liquid-Phase Selective Hydrogenation of Phenylacetylene

Abstract  

An ultra-large pore mesocellular foam silica (MCF) was employed as a support for preparation of supported Pd catalysts for the liquid-phase selective hydrogenation of phenylacetylene. The catalysts were prepared by three different routes: (i) incipient wetness impregnation using Pd(II)acetate solution (Pd/MCF-imp), (ii) impregnation of colloidal Pd nanoparticles obtained by the solvent reduction method (Pd/MCF-col), and (iii) in situ synthesis of MCF in the presence of the Pd colloid (Pd/MCF-ss). The conventional impregnation method resulted in more agglomeration of Pd particles and partial collapse of MCF structure, hence the Pd/MCF-imp exhibited the lowest selectivity towards styrene at total conversion of phenylacetylene. Only the Pd/MCF-ss, in which most of the Pd nanoparticles were encapsulated by the silica matrix, was found to retain high styrene selectivity (>80%) after complete conversion of phenylacetylene. Comparing to the other highly efficient Pd catalysts reported in the literature under similar reaction conditions, it can be emphasized that coverage of Pd surface by the support produces great beneficial effect for enhancing styrene selectivity, regardless of the type of supports used (i.e., TiO₂, carbon nanotubes, or mesostructured silica).     

Promotional SMSI Effect on Supported Palladium Catalysts for Methanol Synthesis

High-temperature reduction (HTR) of palladium catalysts supported on some reducible oxides, such as Pd/CeO₂, and Pd/TiO₂ catalysts, led to a strong metal-support interaction (SMSI), which was found to be the main reason for their high and stable activity for methanol synthesis from hydrogenation of carbon dioxide. But low-temperature-reduced (LTR) catalysts exhibited high methane selectivity and were oxidized to PdO quickly in the same reaction. Besides palladium, platinum exhibited similar behavior for this reaction when supported on these reducible oxides. Mechanistic studies of the Pd/CeO₂ catalyst clarified the promotional role of the SMSI effect, and the spillover effect on the HTR Pd/CeO₂ catalyst. Carbon dioxide was decomposed on Ce₂O₃, which was attached to Pd, to form CO and surface oxygen species. The carbon monoxide formed was hydrogenated to methanol successively on the palladium surface while the surface oxygen species was hydrogenated to water by spillover hydrogen from the gas phase. A reaction model for the hydrogenation of carbon dioxide was suggested for both HTR and LTR Pd/CeO₂ catalysts. Methanol synthesis from syngas on the LTR or HTR Pd/CeO₂ catalysts was also conducted. Both alcohol and hydrocarbons were formed significantly on the HTR catalyst from syngas while methanol formed predominantly on the LTR catalyst. Characterization of these two catalysts elucidated the reaction performances.     

Catalytic hydrogenation of linoleic acid over platinum-group metals supported on alumina

Catalytic activity and selectivity for hydrogenation of linoleic acid (cis-9,cis-12 18:2) were studied on Pt, Pd, Ru, and Ir supported on Al₂O₃. Stearic acid (18:0) and 10 different octadecenoic isomers (18:1) in the products could be separated completely by using a new capillary column coated by isocyanopropyl trisilphenylene siloxane for gas-liquid chromatography. The monoenoic acid isomers and dienoic acid isomers in the products on the various catalysts showed different distributions. The catalysts exhibited nearly equal selectivity for stearic acid formation. The 12-position double bond in linoleic acid has higher reactivity than the 9-position double bond in catalytic hydrogenation on platinum-group metal catalysts. In addition to hydrogenation products of linoleic acid, geometrical and positional dienoic acid isomers (trans-9,trans-12; trans-8,cis-12; cis-9,trans-13; trans-9,cis-13; cis-9,trans-12 18:2), due to isomerization of linoleic acid during hydrogenation, were contained in the reaction products. Ru/Al₂O₃ exhibited the highest activity for isomerization of linoleic acid with the noble metal catalysts. Conjugated octadecadienoic acid isomers have been observed in products of the reaction on Pt/Al₂O₃, Ru/Al₂O₃, and Ir/Al₂O₃. Catalytic activities of noble metals for positional and geometric isomerization of linoleic acid during hydrogenation decreased in the sequence of Ru ≥ Pt > Ir » Pd.     

Surface Modification of Pd/α-Si3N4 Catalysts Through the Solvent Used During Synthesis. Implications on the CO Chemisorption Properties and Catalytic Performances

Palladium catalysts supported on α-Si₃N₄ were prepared by impregnation with Pd(II)-acetate dissolved either in toluene or in water. The mean metal particle size of ~0.5 wt% Pd catalysts was similar (~5 nm) and independent of the way of preparation. Nevertheless, the two catalysts present very different chemisorption behaviour chemisorptive and catalytic properties. Fourier transformed infrared (FTIR) spectra of adsorbed CO at different temperatures (ranging from room temperature to 300 °C) show a very different behaviour for both catalysts. While the CO adsorption states on the Pd/α-Si₃N₄ prepared in toluene are very similar to those generally measured for silica and/or alumina supported palladium catalysts, CO chemisorbs less strongly on Pd/α-Si₃N₄ prepared in water and on different adsorption sites. The Pd/α-Si₃N₄ catalyst obtained by aqueous impregnation is much less efficient for the methane total oxidation. It is less active and less stable: it deactivates strongly after 3 h on stream at 650 °C. The two catalysts present about the same activity for the 1,3-butadiene hydrogenation after stabilisation at 20 °C. But, the catalyst prepared in water shows a much better selectivity to butenes. The results are discussed in terms of the possible migration of silicon atoms from the silicon nitride support to the surface of the palladium particles, when the catalyst is prepared in water. This is not the case when prepared in an organic solvent.     

Effect of Metal Type on Partial Hydrogenation of Rapeseed Oil-Derived FAME

Supported SiO₂ catalysts were studied for the partial hydrogenation of rapeseed oil-derived fatty acid methyl esters (FAME) for improving its oxidative stability. The effect of metal type: Pt, Pd, and Ni, on catalytic activity and cis–trans selectivity was investigated. Hydrogenation activity was studied in terms of turn over frequency (TOF) of C18:3, C18:2, C18:1, and C18:0 FAME. The highest TOF of C18:3, C18:2, and C18:1 was found for Pd catalyst. However, C18:0 TOF of Pt is higher than that of the Pd catalyst. The higher in C18:0 TOF can explain the low selectivity towards trans-monounsaturated FAME of the Pt catalyst, which is due to the subsequent hydrogenation of the intermediate trans-monounsaturated to saturated FAME. On the other hand, Ni showed the lowest TOFs when compared with the Pt and Pd catalysts.     

Nanosized Pd/Pt and Pd/Rh Catalysts for Naphthalene Hydrogenation and Hydrogenolysis/Ring-opening

Pd/Rh and Pd/Pt catalysts supported on two different mesoporous materials – a Zr-doped MCM-41-type silica [Si/Zr = 5 w/w (SiZr)] and a commercial silica-alumina [Si/Al = 40:60 w/w (SiAl)] – were prepared by incipient wetness impregnation using nanosized suspensions of alloy particles prepared by polyol-mediated synthesis in diethylene glycol (DEG). The catalytic behaviour of these catalysts was investigated in the hydrogenation and hydrogenolysis/ring-opening of naphthalene at 6.0 MPa, by checking the role of both the main reaction conditions (temperature, contact time and H₂/naphthalene molar ratio) and increasing amounts of dibenzothiophene (DBT). The catalysts supported on SiAl showed higher activity than catalysts supported on SiZr, thus suggesting that activity is favoured by higher acidity of the support and/or higher interaction of the nanosized metal particles with the support. While using the SiZr support, weaker metal-support interactions took place by forming catalysts with bigger metal and/or metal oxide particles. Besides, the catalyst with lowest noble-metal content (0.3 wt.%) (SiAl-0.3Pd/Pt-5) had the greatest acidity and metal surface and, consequently, the highest activity. Furthermore, it exhibited a good thiotolerance in presence of increasing amounts of DBT in the feed, thus maintaining a high catalytic activity in the hydrogenation of naphthalene, although with decreased yield in trans- and cis-decalin (decahydronaphthalene or DeHN) and high-molecular-weight compounds (H.M.W.), with a corresponding increased yield in the partially hydrogenated tetralin (tetrahydronaphthalene or TeHN).     

Polymer‐based catalysts for toluene hydrogenation

Crosslinked poly(4‐vinylpyridine‐co‐styrene) was synthesized by radical polymerization. Catalysts having 1 wt % Pd were obtained by impregnation of a copolymer, poly(4‐vinylpyridine‐co‐styrene) with a Pd colloidal dispersion. We modified metal particle sizes by changing the aging period of the colloidal dispersion, with the average size in the range of 2.5–4.3 nm. The most probable structure of the metal cluster attached to the polymers is described. X‐ray diffraction, transmission electron microscopy (TEM), and H₂? O₂ titrations were used as characterization techniques. The H₂ consumption during titration was extremely low, and the calculated metal dispersion was between 15 and 25 times lower than those estimated from TEM. This suggests that the Pd crystals were almost completely covered by the polymer. The vapor‐phase hydrogenation of toluene on resins supported Pd catalysts were studied. The catalysts in the hydrogenation of toluene exhibited low activity, and the obtention of significant selectivities to partial hydrogenation products (close to 60 mol %) was remarkable. The results are explained in terms of a significant decrease in the hydrogenation capacity due to the coverage of metal particles by the resin. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 381–385, 2002     

Pd and Pt catalysts supported on carbon-coated monoliths for low-temperature combustion of xylenes

Carbon-coated monoliths were prepared from polyfurfuryl alcohol coated cordierite structures obtained by dip-coating. In this way, thin, homogeneous, consistent and good adhered carbon layers were obtained. The different steps followed in the preparation of these catalyst supports were studied by scanning electron microscopy. Pd and Pt catalysts were prepared by equilibrium impregnation of the monolithic supports with an aqueous solution of the corresponding tetraammine metal (II) nitrates. The catalysts were pretreated in H₂ at 300 °C before their characterization by chemisorption or before testing their catalytic activity. This pretreatment was monitored by temperature programme reduction. Catalytic activities in xylene combustion were evaluated as a function of the reaction temperature as well as against time on stream. The monolithic catalysts were thermally stable during the reaction. The Pt catalysts were more active than the Pd ones. The Pd catalysts with smaller Pd-particle sizes were more active. In the case of Pt catalysts however, the opposite was observed, which might be due to a structure sensitivity effect. Complete xylene combustion was reached in the range between 150 and 180 °C with a total selectivity to CO₂ and H₂O. Combustion of m-xylene was easier than p-xylene over Pt.     

Catalytic hydrogenation of nitrile rubber using palladium and ruthenium complexes

The catalytic hydrogenation of acrylonitrile‐butadiene copolymer (nitrile rubber, NBR) using Pd(OAc)₂ or RuCl₂(PPh₃)₃ catalysts has been investigated in order to produce a totally saturated nitrile rubber. The hydrogenation of NBR is effective with both catalysts and achieved total conversion under the appropriate reaction conditions. In the case of palladium the effects of reaction parameters such as reaction temperature, pressure, time, catalyst concentration, and NBR concentration have been investigated. Even though both ruthenium‐ and palladium‐based catalysts are effective in the production of HNBR, the former requires harsh reaction conditions and has the drawback of gel formation under high conversion, motivating the migration to RuCl₂ (PPh₃)₃ as an alternative catalyst. The degree of hydrogenation was determined by IR and NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Kinetics-assisted identification and regulation of active sites for Pd-catalyzed propyne selective hydrogenation

Identification and regulation of active sites are significant for guiding the design and optimization of hydrogenation catalysts toward the target product but remain a great challenge. Herein, we demonstrate a kinetics-assisted identification method combined with theoretical calculations for identifying and further regulating the dominant active sites of Pd catalysts for propyne hydrogenation. Kinetics analysis and model calculations based on the cuboctahedron shape of Pd nanoparticles in the catalysts indicate the Pd(111) sites as the dominant active sites for the propyne conversion and propylene formation while the Pd(100) sites as those for the propane formation, which are further rationalized by theoretical calculations. Moreover, the Pd catalyst with electron-rich properties exhibits relatively higher activity and selectivity, guided by which the SiO₂ support with abundant electron-donating hydroxyl groups is employed to increase the Pd electron density. Such electronic regulation for the Pd catalyst clearly enhances the selective hydrogenation of propyne.