Nickel Phosphide Phase Research Articles

Probing Mixed Phase Metallic Ni/Amorphous Nickel Phosphide Nanocatalysts during Oxygen Evolution Reaction Using Operando X-Ray Absorption Spectroscopy

Metal phosphide-containing nanomaterials have demonstrated remarkable efficacy as non-precious metal-based catalysts for the alkaline oxygen evolution reaction (OER). While it is widely acknowledged that various OER catalysts undergo structural reconstruction under applied OER potentials, monitoring these changes is challenging because they are often rapid and require instrumentation not typically found in the typical lab setting. In this study, we utilize operando X-ray absorption spectroscopy (XAS) to determine the structural reconstruction of nickel-based metal phosphide catalysts during OER. We have developed the synthesis of nickel-based phosphide nanoparticles with a range of phosphorus incorporation. These nanoparticles are composed of metallic nickel and amorphous nickel phosphide phases as determined by XRD, TEM and XAS. At low levels of P incorporation, from 2% to 15%, the synthesis results in the mixture of metallic nickel and amorphous phosphide phases. At higher levels of phosphorus incorporation, from 20% to 30%, amorphous nickel phosphide is the predominant phase. Electrochemical characterization of this nickel phosphide series for OER revealed that the catalysts with 20% phosphorus incorporation exhibited superior OER activity. The phosphides with lower phosphorus content, such as 2%, had smaller Ni2+/Ni3+ redox peaks which has been shown to suppress the conversion to Ni(OH)2, leading to lowered OER activity. Increased amorphous nickel phosphide phase led to greater activity, suggesting that the active component in the catalyst comes from the amorphous nickel phosphide phase. Meanwhile, higher phosphorus content (20-30%) where the amorphous phosphide is the predominate phase resulted in larger redox peaks, signifying greater conversion to Ni(OH)2. Operando XAS will be applied to investigate these metallic nickel/nickel phosphide nanocatalysts to elucidate their structural reconstruction during OER

Tribological behavior of autocatalytic Ni-P based duplex coatings

The present research evaluates the tribological performance of different Ni-P based duplex autocatalytic coatings (electroless coatings). The study investigates coatings including Ni-P/Ni-W-P, Ni-P/Ni-Mo-P, and Ni-P/Ni-Cu-P, examining various factors such as heat treatment conditions, sample composition, and their influence on the coatings’ performance. The phase structure of the coatings is influenced by heat treatment parameters viz. temperature and duration as well as phosphorus content. Notably, at temperatures above 400 °C, all duplex coatings form a robust nickel phosphide phase, enhancing hardness and wear resistance which is almost double of that in as-deposited state in some cases. When subjected to a temperature of 400 °C for duration of 1 h, the Ni-P/Ni-W-P coating displays the highest microhardness (1440 HV0.1) and the lowest wear rate (10.62 × 10−5. mm3. N−1. m−1) among all the duplex coatings. In all three duplex systems, the wear typically involves a combination of abrasive and adhesive mechanisms. Among the as-deposited coatings, the Ni-P/Ni-Cu-P demonstrates higher corrosion potential (E corr −302 mV) and lower corrosion current (i corr 1.83 × 10−5 mA cm−2) which imply superior corrosion resistance compared to the other duplex coatings. In the heat-treated state, the Ni-P/Ni-Mo-P duplex coating generally exhibits better corrosion resistance when compared to the other two types of duplex coatings.

Experimental optimization of Ni/P atomic ratio for nickel phosphide catalysts in reverse water-gas shift

Nickel phosphide catalysts show a high level of selectivity for the reverse water-gas shift (RWGS) reaction, inhibiting the competing methanation reaction. This work investigates the extent to which suppression of methanation can be controlled by phosphidation and tests the stability of phosphide phases over 24-hour time on stream. Herein the synthesis of different phosphide crystal structures by varying Ni/P atomic ratios (from 0.5 to 2.4) is shown to affect the selectivity to CO over CH4 in a significant way. We also show that the activity of these catalysts can be fine-tuned by the synthesis Ni/P ratio and identify suitable catalysts for low temperature RWGS process. Ni12P5-SiO2 showed 80–100% selectivity over the full temperature range (i.e., 300–800 °C) tested, reaching 73% CO2 conversion at 800 °C. Ni2P-SiO2 exhibited CO selectivity of 93–100% over a full temperature range, and 70% CO2 conversion at 800 °C. The highest CO2 conversions for Ni12P5-SiO2 at all temperatures among all catalysts showed its promising nature for CO2 capture and utilisation. The methanation reaction was suppressed in addition to RWGS activity improvement through the formation of nickel phosphide phases, and the crystal structure was found to determine CO selectivity, with the following order Ni12P5 >Ni2P > Ni3P. Based on the activity of the studied catalysts, the catalysts were ranked in order of suitability for the RWGS reaction as follows: Ni12P5-SiO2 (Ni/P = 2.4) > Ni2P-SiO2 (Ni/P = 2) > NiP-SiO2 (Ni/P = 1) > NiP2-SiO2 (Ni/P = 0.5). Two catalysts with Ni/P atomic ratios; 2.4 and 2, were selected for stability testing. The catalyst with Ni/P ratio = 2.4 (i.e., Ni12P5-SiO2) was found to be more stable in terms of CO2 conversion and CO yield over the 24-hour duration at 550 °C. Using the phosphidation strategy to tune both selectivity and activity of Ni catalysts for RWGS, methanation as a competing reaction is shown to be no longer a critical issue in the RWGS process for catalysts with high Ni/P atomic ratios (2.4 and 2) even at lower temperatures (300–500 °C). This opens up potential low temperature RWGS opportunities, especially coupled to downstream or tandem lower temperature processes to produce liquid fuels.

Evaluating the Effect of Laser Surface Modification on the Corrosion Behavior of Ni-P-SiC Electroless Coating Deposited on Al356 Alloy

Regarding their higher wear/corrosion resistance than conventional coatings, nickelphosphorus based composite coatings can reduce components’ costs and degradation. This study employed laser surface modification of Ni-P-SiC electroless coatings deposited on Al356 substrate, followed by investigating their microstructural changes and corrosion behavior. The results showed that increasing the laser power increases surface defects and causes substrate diffusion to the coating, which significantly reduces the corrosion resistance of the coating. In contrast, low-power laser operations can improve the corrosion resistance of Ni-P-SiC composite coatings by creating stable nickel phosphide phases, more uniform element distribution, and enhanced SiC particle-substrate coherence. All these factors increase the wear and corrosion resistance simultaneously.

Production of bio-paraffin from solvent-free deoxygenation of palm biodiesel over ZrO2-supported nickel phosphide catalysts

This study investigated the effects of Ni/P molar ratio on nickel phosphide species and on the catalytic activity on solvent-free deoxygenation of palm biodiesel to produce n-paraffins. ZrO2-supported nickel phosphide catalysts with different Ni/P molar ratio were synthesized and characterized through HRTEM, XPS, XRD, BET, NH3-TPD, and H2-TPR analysis techniques, to give an insight into the correlation of the catalyst structure and its performance. The formation of different types of nickel phosphide phases when preparing the catalyst with different Ni/P molar ratio was observed. Only Ni2P was formed with Ni/P molar ratio of 1, while Ni2P and Ni12P5 were detected when Ni/P molar ratio was 2. With further increasing Ni/P molar ratios to 3 and 4, new phases of Ni0 and Ni3P were formed in addition to those of Ni2P and Ni12P5. NixP/ZrO2 exhibited excellent catalytic performance for deoxygenation of palm biodiesel mainly via decarbonylation/decarboxylation pathways, achieving the high FAME conversion of 50.2–88.0% and n-alkane selectivity of 65.0–95.4%. Conversion and alkane selectivity of the catalysts followed the sequence: Ni3P/ZrO2 ≈ Ni4P/ZrO2 > Ni2P/ZrO2 > Ni1P/ZrO2 > Ni/ZrO2, respectively. These results suggested that Ni/P molar ratio had significantly affected on catalytic performance, which was associated with the type of nickel phosphide phase, metal dispersion, metal particle size, as well as electron density on Ni site.

Ligand-Tuned Energetics for the Selective Synthesis of Ni2P and Ni12P5 Possessing Bifunctional Electrocatalytic Activity toward Hydrogen Evolution and Hydrazine Oxidation Reactions.

The occurrence of many phases and stoichiometries of nickel phosphides calls for the development of synthetic levers to selectively produce phases with purity. Herein, thiol (-SH) and carboxylate (-COO-) functional groups in ligands were found to effectively tune the energetics of nickel phosphide phases during hydrothermal synthesis. The initial kinetic product Ni2P transforms into thermodynamically stable Ni12P5 at longer reaction times. The binding of carboxylate onto Ni2P promotes this phase transformation to produce pure-phase Ni12P5 within 5 h compared to previous reports (∼48 h). Thiol-containing ligands inhibit this transformation process by providing higher stability to the Ni2P phase. Cysteine-capped Ni2P showed excellent geometric and intrinsic electrocatalytic activity toward both hydrogen evolution and hydrazine oxidation reactions under alkaline conditions. This bifunctional electrocatalytic nature enables cysteine-capped Ni2P to promote hydrazine-assisted hydrogen generation that requires lower energy (0.46 V to achieve 10 mA/cmgeo2) compared to the conventional overall water splitting (1.81 V to achieve 10 mA/cmgeo2) for hydrogen generation.

Alcohol oxidation with high efficiency and selectivity by nickel phosphide phases

Ni12P5nanoparticles are used for electro-oxidation of various alcohols through a preferred reaction path, by O–H activation, that supresses futher oxidation to CO2and produces valuable chemicals.

Duplex electroless Ni-P/Ni-P-W coatings: Effect of heat treatment on tribological and corrosion performance

The current study attempts to investigate the effect of heat treatment on duplex electroless Ni–P/Ni–W-P coatings. Duplex electroless Ni-P/Ni–W-P coatings are produced on mild steel and heat-treated for 2 h at temperatures ranging from 200 to 800 °C. A pin-on-disc arrangement is used to test the friction and wear characteristics of the as deposited and heat-treated coatings. The microstructural aspects are studied, viz. surface morphology, composition and the crystallographic structure. Heat-treatment at 400 °C for a two-hour duration produces the maximum hardness due to the formation of the crystalline nickel phosphide (Ni3P) phase. The friction and wear performance of the coating seems to be diminishing at higher temperatures due to the formation of oxides and grain coarsening. Corrosion tests on duplex coatings reveal better corrosion resistance for coating with Ni–W-P as the outer layer.

Synthesis and Composition Study of Electrochemically Deposited Ni-P Coating with Increased Surface Area

Nickel phosphides NixPy are a promising family of binary compounds that have shown much promise in various fields of technology, including energy storage, light absorption and heterogeneous catalysis in the reactions of biomass hydrogenation. The performance of NixPy-containing materials depends greatly on their morphology and phase composition and, in turn, on the synthesis technique. In this work, we have employed the electroplating approach to synthesize a Ni-P coating, which was treated with nitric acid in order to develop its surface area and enrich it with phosphorus. We have employed scanning electron microscopy, X-ray diffraction and 31P nuclear magnetic resonance techniques to characterize the particles separated from the coating with ultrasound for the convenience of the study. According to experimental data, the obtained powder contained a mixture of Ni3P and phosphorus oxides, which transformed into nickel phosphide phases richer with phosphorus, such as Ni5P2 and Ni12P5, after treatment at elevated temperatures. Thus, we have demonstrated that electroplating followed by acid treatment is a feasible approach for the synthesis of Ni-P coatings with increased surface area and variable phase composition.

Furfural hydrodeoxygenation (HDO) over silica-supported metal phosphides – The influence of metal–phosphorus stoichiometry on catalytic properties

The gas-phase hydrodeoxygenation (HDO) of furfural, a model compound for bio-based conversion, was investigated over transition metal phosphide catalysts. The HDO activity decreases in the order Ni2P ≈ MoP > Co2P ≈ WP ≫ Cu3P > Fe2P. Nickel phosphide phases (e.g., Ni2P, Ni12P5, Ni3P) are the most promising catalysts in the furfural HDO. Their selectivity to the gasoline additives 2-methylfuran and tetrahydro-2-methylfuran can be adjusted by varying the P/Ni ratio. The effect of P on catalyst properties as well as on the reaction mechanism of furfural HDO were investigated in depth for the first time. An increase of the P stoichiometry weakens the furan-ring/catalyst interaction, which contributes to a lower ring-opening and ring-hydrogenation activity. On the other hand, an increasing P content does lead to a stronger carbonyl/catalyst interaction, i.e., to a stronger η2(C, O) adsorption configuration, which weakens the C1O1 bond (Scheme 1) in the carbonyl group and enhances the carbonyl conversion. Phosphorus species can also act as Brønsted acid sites promoting C1O1 (Scheme 1) hydrogenolysis of furfuryl alcohol, hence contributing to higher production of 2-methylfuran.

The defining role of phosphorous on microstructure, nanohardness and thermal stability of pulsed electrodeposited nanocrystalline nickel-phosphorous alloys

Free-standing nanocrystalline (NC) nickel-phosphorous (Ni–P) alloy foils with P content in the range of 0.2–5.0 wt percent are synthesized by pulsed electrodeposition technique. The aim of the present study is to evaluate the effect of P content on the hardness and microstructural evolution in Ni–P alloys during both electrodeposition and thermal treatment. The microstructure, hardness and thermal analysis of the alloys are investigated using electron microscopy, nanoindentation and differential scanning calorimetry (DSC), respectively. This study demonstrates that there is localized structural heterogeneity in conjunction with significant grain refinement in the alloys containing excessive P content beyond its solid solubility. Nanohardness measurements indicate that both the grain refinement and internal strain induced by codeposition of P solute atoms affect the strengthening of Ni matrix. The exothermic peaks observed in the DSC thermograms are found to be strongly dependent on P content in the alloy and these are associated with structural relaxation, formation of metastable and stable nickel phosphide phases along with concurrent grain growth and particle coarsening. The grain growth kinetics study showed that in Ni–P alloys Smith-Zener drag mechanism involving control of grain boundary mobility by Ni3P nanoparticles overtakes the solute drag effect of P with increasing temperature.

Improving the HER Kinetics of the Nickel Phosphide Catalyst Using Electrochemical Dealloying Treatment

Hydrogen fuel is receiving a lot of attention owing to its high efficiency and eco-friendliness. The reforming of natural gas is conventionally used to generate hydrogen gas; however, the process generates carbon dioxide causing global warming. To solve the problem, water electrolysis, which produces hydrogen and oxygen gas from water, is actively studied in order to design a cheaper and more effective hydrogen generation system.The major research gap of water electrolysis is the high cost due to the rarity of catalyst materials such as platinum [1,2]. As a substitute for a platinum catalyst, transition metal phosphides represented by nickel phosphide (Ni-P) has shown the comparable catalytic activity to platinum, despite the much lower cost compared to platinum. The nickel phosphide can be fabricated with a facile electroplating process which can be more suitable synthesis process of electrocatalyst, because it is not necessary to mix with a polymer such as Nafion, disturbing emission of generated gas and decreasing surface area [3]. On the other hand, the nickel phosphide has showed low stability in acid media. According to the previous researches [4], the main reason of low stability is due to the difference of corrosion potential between nickel metal and Ni-P phases. Furthermore, they suggest three strategies to increase the corrosion resistance: (i) well-alloying of nickel and phosphorus, (ii) formation of amorphous film at grain boundary, and (iii) formation of phosphate passive film on the surface [4].In this context, we adopted the electrochemical surface treatment for the electroplated Ni-P to improve the activity and stability of Ni-P/carbon paper (CP) catalyst. The surface treatment (“dealloying surface treatement”) is to remove the ‘isolated Ni’ which has less bonding with P, which is composed of the CV cycles inducing the repetition of oxidation and reduction of Ni-P/CP catalyst. Furthermore, it is expected to form well-alloying between nickel and phosphide (recrystallization of Ni-P).As a result, the morphology of Ni-P/CP after CV 20 cycles was similar with raw Ni-P/CP as shown in Fig. 1a, b. However, an area of P-rich portion (dark part) increased after dealloying cycles. Therefore, an atomic ratio of phosphorus increased about 186% higher after 20 cycles of CV than the Ni-P/CP which did not conduct surface treatment. In addition, the more invasion of phosphorus atom aroused a decrease of grain size of nickel metal (Fig. 1c). According to XPS data of Ni state in Fig. 1d, an intensity of peak at a binding energy of 853 eV which means a bonding of Ni2P increased after the dealloying process. That is, the bonding between Ni and P atoms increased after the treatment. An atomic ratio of P at the surface was also increased to 36.54at%, since Ni-P/CP catalyst showed 24.88at% of P. As a result, a repetition of reduction and oxidation of Ni-P during the dealloying surface treatment decreases the cystalline size of Ni and increase the P content of the Ni-P catalyst.Due to such the changes, the Ni-P/CP showed a higher activity and stability after the dealloying surface treatment. Specifically, Ni-P/CP after CV 20 cycles showed the highest HER activity, with the overpotential of 124 mV at the current density of 10 mA cm-2, since raw Ni-P/CP had the overpotential of 179 mV (Fig. 2a). And then, the current density for Ni-P/CP after CV 20 cycles was maintained at approximately 80.4% at −0.2 VRHE for 6 hours, while raw Ni-P/CP maintained a current density of 35.6%. It is presumably because the nickel atoms can use enough electrons for the HER, which is provided from well –bonded phosphorus atoms [5].

Catalytic system based on nickel(II) acetate and hypophosphorous acid for the selective hydrodeoxygenation of guaiacol

The title catalytic system exhibited high activity in the hydrogenation–hydrodeoxygenation of guaiacol (a low-molecular-weight product of lignin degradation). The conversion of guaiacol reached 97%, and the selectivity for cyclohexane was as high as 94%. Nickel phosphide phases were obtained in the reaction medium, and their presence determined the high activity of the catalytic system in the hydroconversion of guaiacol.

Nickel Phosphinidene Molecular Clusters from Organocyclophosphine Precursors.

We report a new family of nickel phosphinidene molecular clusters synthesized from the reaction of bis(1,5-cyclooctadiene)nickel(0) ([Ni(cod)2 ]) with organocyclophosphine and trialkylphosphine. We found that [Ni(cod)2 ] cleaves the organocyclophosphine P-P bonds to generate phosphinidene groups, establishing the cyclic molecules as valuable precursors for making charge-neutral molecular clusters passivated by two-electron donor capping ligands. The formation of the cluster core structure is controlled by the bulkiness of the precursor and of the capping ligand. As a demonstration of this new cluster-forming reaction, we describe three clusters with different core nuclearity and degree of ligation: Ni12 (PMe)10 (PEt3 )8 , Ni8 (PMe)6 (PMe3 )8 , and Ni8 (PiPr)6 (PMe3 )6 . In addition, we show that the larger cluster, Ni12 (PMe)10 (PEt3 )8 , can be used as a low temperature single-source molecular precursor to the catalytically active nickel phosphide phase Ni2 P.

Nanostructured nickel phosphide as an efficient photocatalyst: Effect of phase on physical properties and dye degradation

Nickel phosphide nanostructures are synthesized by hydrothermal method. The effect of different nickel phosphide phases on structural, morphological, and optical properties as well as photocatalytic performance are investigated. XRD results show that initially, the Ni12P5 phase is formed, then by increasing the P/Ni molar ratio in the starting solution, product phase gradually transforms to the Ni2P phase. The results showed that crystalline phase and morphology of the nanostructures affects the catalytic performance of the samples. The best result for methylene blue dye removal was achieved for the sample with 35/1 phosphorus to nickel molar ratio which had pure Ni2P phase.

Support Effect on the Performance of Ni2P Catalysts in the Hydrodeoxygenation of Methyl Palmitate

The effect of support nature, SiO2 and γ-Al2O3, on physicochemical and catalytic properties of nickel phosphide catalysts in methyl palmitate hydrodeoxygenation (HDO) has been considered. Firstly, alumina-supported nickel phosphide catalysts prepared by temperature-programmed reduction method starting from different precursors (phosphate–Ni(NO3)2 and (NH4)2HPO4 or phosphite–Ni(OH)2 and H3PO3) were compared using elemental analysis, N2 physisorption, H2-TPR, XRD, TEM, NH3-TPD, 27Al and 31P MAS NMR techniques and catalytic experiments. The mixture of nickel phosphide phases was produced from phosphate precursor on alumina while using of phosphite precursor provides Ni2P formation with the higher activity in methyl palmitate HDO. Besides, the comparative study of the performances of Ni2P/SiO2 and Ni2P/Al2O3 catalysts demonstrates the apparent superiority of alumina-supported Ni2P in the methyl palmitate hydrodeoxygenation. Considering the tentative scheme of methyl palmitate transformation, we proposed that cooperation of Ni2P and acid sites on the surface of alumina provides the enhanced activity of alumina-supported Ni2P through the acceleration of acid-catalysed hydrolysis.

Effect of P/Ni ratio on the performance of nickel phosphide phases supported on zirconia for the hydrodeoxygenation of m-cresol

The catalytic performances of various nickel phosphide catalysts (NiP) supported on ZrO2 synthesized with different P/Ni molar ratios (0.8, 2 and 3) were investigated in hydrodeoxygenation (HDO) of m-cresol at 340 °C under 4 MPa. The solid sample with the highest P/Ni ratio (NiP-3/ZrO2) presented the best catalytic performances in terms of activity, which were attributed to the presence of the pure Ni2P phase, the other samples containing either a mixture of Ni2P and Ni12P5 (NiP-2/ZrO2) or Ni12P5 (NiP-0.8/ZrO2) alone were less active. The use of ZrO2 as support required a large excess of P to obtain Ni2P as active phase.

Phase Diversity of Nickel Phosphides in Oxygen Reduction Catalysis

AbstractMotivated by the challenge to find a low‐cost catalyst with high activity for the oxygen reduction reaction (ORR), transition metal phosphides (TMPs) appear to be one of the most burgeoning alternatives to noble metal based electrocatalysts. In addition to the low cost, TMPs have numerous interesting features such as high conductivity and chemical stability. Since, the catalytic activity of TMPs is highly dependent on the metal/phosphorous ratio, herein, we report the investigation of nickel‐phosphide/carbon composites of different stoichiometries (NixPy/C) with tractable nickel phosphide phases as promising electrocatalyst for ORR under alkaline and acidic conditions. The NixPy/C composites are obtained by carbonization of a Ni‐struvite (NiNH4PO4 ⋅ H2O) coated phenol‐formaldehyde resin at different temperatures, resulting in variations of the formed NixPy phases. As expected, it is found that the electrocatalytic ORR performance of the NixPy/C composites highly depends on the predominant phase of nickel phosphide formed. The highest catalytic activity for ORR in alkaline as well as acidic media was found for the NixPy/C composite with the highest proportion of Ni2P as a predominant phase, obtained at 800 °C. For composites with NiP2 and Ni12P5 as the predominant phase, obtained at lower and higher temperatures, respectively, a lower catalytic activity was found.

Preparation and characterization of a supported system of Ni2P/Ni12P5 nanoparticles and their use as the active phase in chemoselective hydrogenation of acetophenone

Ni2P/Ni12P5 nanoparticles were obtained by thermal decomposition of nickel organometallic salt at low temperature. The use of different characterization techniques allowed us to determine that this process produced a mixture of two nickel phosphide phases: Ni2P and Ni12P5. These nickel phosphides nanoparticles, supported on mesoporous silica, showed activity and high selectivity for producing the hydrogenation of the acetophenone carbonyl group to obtain 1-phenylethanol. This is a first report that demonstrates the ability of supported Ni2P/Ni12P5 nanoparticles to produce the chemoselective hydrogenation of acetophenone. We attribute these special catalytic properties to the particular geometry of the Ni–P sites on the surface of the nanoparticles. This is an interesting result because the nickel phosphides have a wide composition range (from Ni3P to NiP3), with different crystallographic structures, therefore we think that different phases could be active and selective to hydrogenate many important molecules with more than one functional group.

Nondestructive construction of Lewis acid sites on the surface of supported nickel phosphide catalysts by atomic-layer deposition

In this paper, we have developed a new strategy to construct the acidic sites on the surface of supported transition-metal phosphide catalysts, which could precisely control the deposition of the Al2O3 atomic layer through atomic-layer deposition (ALD). A series of supported nickel phosphide catalysts decorated with Al2O3 film were prepared and characterized. The results show that Al2O3 film was deposited on the surface of the catalyst via AlOSi bonding, which does not affect or alter the characteristics of the as-prepared nickel phosphide phase. Most importantly, among all the Ni2P-based catalysts, the Ni2P/SiO2-ALD catalyst with 10 Al2O3 layers possesses the optimal performance in hydrodesulfurization and hydrodearomatization reactions. In particular, superior hydrogenation performances were considered to be strongly related to a synergistic effect between nickel phosphide and the modulated acidic property. This precise stepwise ALD strategy opens a convenient route and provides a prospective design guideline for constructing high-performance hydrogenation catalysts.