Catalyst For Liquid-phase Hydrogenation Research Articles

Probing the core and surface composition of nanoalloy to rationalize its selectivity: Study of Ni-Fe/SiO2 catalysts for liquid-phase hydrogenation

Rationalization of the catalytic performance of bimetallic Ni-Fe catalysts in selective hydrogenation reactions is based on the Ni and Fe distribution within the nanoparticles and at their surface. By applying a combination of element-specific and surface-specific characterization techniques ( 57 Fe Mössbauer spectroscopy, X-ray absorption spectroscopy, and low-energy ion scattering) to a series of Ni-Fe/SiO 2 catalysts differing by their Ni and Fe molar proportions, we showed that reduced Ni-Fe nanoparticles exhibit a gradient of Ni concentrations from a Ni-enriched core to Ni-depleted, Fe-enriched outer shells. A surface proportion of 35–45 Ni atom % showed the highest yield of furfuryl alcohol in liquid-phase hydroconversion of furfural. These results point to the need for Ni surface domains of limited size among Fe atoms to restrict the hydroconversion process to its first stage rather than to nominal compositions of the catalyst or to surface sites that would appear to be particularly selective per se. • Bimetallic Ni-Fe catalysts in hydrogenation of furfural were extensively studied • Fe as a promoter of Ni increases catalyst selectivity and its stability • Ni concentration changed from Ni-enriched core to Ni-depleted, Fe-enriched outer shells • Limited-size Ni domains among Fe atoms permit control of the hydrogenation process Bimetallic catalysis for conversion of bio-sourced molecules has often relied on noble metals that should be replaced in the near future by the association of cheaper and more abundant base metals, also known by a poor Z-contrast, which makes in-depth characterization of these systems challenging. However, determining the distribution of base metals in bimetallic nanoparticles is of paramount importance if one wants to rationalize their selectivity. Besides demonstrating that, despite their oxidable character, Ni-Fe catalysts are stable systems for liquid-phase hydroconversion of furfural, this study demonstrates that heterogeneities in the structure of reduced Ni-Fe nanoparticles are key to understanding their catalytic properties, provides a characterization methodology to discriminate between their surface and core compositions, and determines an adequate balance between the two metals that allows tuning the relative rates of the various reaction pathways and, thus, the selectivity. The synergy between two metals is a key parameter to selectively convert bio-sourced molecules to highly valued chemicals. However, to do that, the distribution of base metals in bimetallic structures must be controlled. We showed that alloying nickel and iron, two of the most common metals, permited us to obtain stable and very active catalyst. A detailed characterization of the materials provides useful insight into the surface composition needed to understand the high catalytic reactivity and selectivity of Ni-Fe structures.

Synthesis and Characterization of Mg-Matrix Based TiO2/Al2O3 Composite Materials

Based on low density, Mg metal-based composites exhibit high specific mechanical properties and are actively used for weight critical structural application. In the present study, Mg-matrix based TiO2/Al2O3 composite materials were synthesized by using the powder metallurgy (Solid-phase) technique. Parameters such as the concentration of the components, temperature, and pressure were optimized before experiments. Different conditions such as temperature (30 °C) and pressure (760 mm of Hg) were also optimized. Pellets of the Mg-based composites and their pure constituent counterparts of various diameters (10–20 cm) were prepared under 50 tons of hydraulic pressure. Single-phase homogenous composites were obtained by undertaking the pellets through sintering in an electric furnace at elevated temperature (600 °C) for 1 h. The prepared materials were tested for different properties using various physicochemical techniques such as Fourier transform infrared spectroscopy (FTIR), Scanning electronic microscopy (SEM), X-ray diffraction (XRD) and Surface area analyzer. FTIR results confirmed composite formation. SEM revealed microstructures of all materials in the µm range. XRD proved the phase-distribution and crystallinity of the prepared materials. It was found that 2 and 3-component systems are homogenized when prepared by the powder metallurgy technique. The surface area of all materials was confirmed using the BET adsorption isotherm equation. The surface area of the prepared composites was found to be in the range from 40 to 70 m2/g. Such properties enable these materials for potential application in solar reflectance and as a catalyst in liquid phase hydrogenation.

Effect of the distribution and dispersion of palladium nanoparticles on the reducibility and performance of Pd/Al2O3 catalyst in liquid-phase hydrogenation of olefins

A series of Pd/γ-Al2O3 catalysts were prepared by wet impregnation method at different pH and time. The effect of metal distribution and dispersion on the catalyst reducibility in liquid-phase hydrogenation of olefins was studied. The samples were characterized by BET, XRD, ICP, FESEM, CO-chemisorption and H2-TPR techniques. Liquid-phase hydrogenation reaction was carried out in a three-phase trickle bed reactor to evaluate the performance of the catalyst samples. The best catalyst performance was attributed to a combination of its desirable characteristics, that is, high reducibility at lower temperatures, high Pd dispersion and an egg-shell Pd distribution which increase the accessibility of the reactants to Pd active sites in this diffusion-limited reaction.

Insights into the Stability of Pd/CN Catalyst in Liquid Phase Hydrogenation of Phenol to Cyclohexanone: Role of Solvent

The production of cyclohexanone by liquid phase phenol hydrogenation is sustainable and green. In this work, the effect of solvent, i.e., water and organic solvents (cyclohexane, methanol and acetone) on the stability of Pd/CN catalyst in the production of cyclohexanone by selective phenol hydrogenation was investigated, and the mechanism is explored by comprehensive characterizations. The results suggest that the solvent has significant effect on the reusability of Pd/CN catalyst in phenol hydrogenation, and the catalytic performance of Pd/CN increases gradually in water but decreases in organic solvents with the reaction cycle. The results of XRD, TEM and XPS confirm that the Pd/CN catalyst maintains wonderful dispersion of Pd NPs and forms more ratio of Pd (0) in water with the reaction cycle, while the opposite results are found in cyclohexane (organic solvents). The results of XPS, TG and BET suggest that the Pd/CN catalyst adsorbs continually phenol in water with the reaction cycle, which inhibits the agglomeration of Pd NPs and promotes the formation of Pd (0), thus better catalytic stability. This work would aid the efficient industrial production of cyclohexanone over Pd/CN. The solvent affected significantly the stability of Pd@CN catalyst in liquid phase phenol hydrogenation to cyclohexanone, and the catalytic activity of Pd@CN increased in water but decreased in cyclohexane with the reaction cycle.

Supported Ni Catalyst for Liquid Phase Hydrogenation of Adiponitrile to 6-Aminocapronitrile and Hexamethyenediamine.

Supported Ni catalysts prepared under different conditions, for liquid phase hydrogenation of adiponitrile (ADN) to 6-aminocapronitrile (ACN) and hexamethyenediamine (HMD), were investigated. The highly reactive imine intermediate can form condensation byproducts with primary amine products (ACN and HMD), which decreased the yield coefficient of primary amines. The catalysts support, condition of catalyst preparation and dosage of additive were studied to improve the yield. A highly dispersed Ni/SiO2 catalyst prepared by the direct reduction of Ni(NO3)2/SiO2 suppressed the condensation reactions by promoting the hydrogenation of adsorbed imines, and it gave the improved hydrogenation activity of 0.63 mol·kgcat−1·min−1 and primary amine selectivity of 94% when NaOH was added into the reactor.

Effect of pretreatment of graphite oxide on activity of platinum supported catalysts in liquid-phase hydrogenation

The effect of the reduction procedure of graphite oxide (GO) on activity of platinum supported catalysts in liquid-phase hydrogenation of nitrobenzene and dec-1-ene was studied. The following methods were applied to prepare the catalysts: simultaneous reduction of graphite oxide and H2PtCl6; deposition of platinum on graphite oxide which was preliminary subjected to reduction with sodium tetrahydroborate or hydrazine hydrate, or to thermal reduction at 1000 and 1050 °С. It was shown that at equal Pt particles size of ca. 2 nm the catalyst supported on thermally reduced graphite oxide is more active in the model reactions than the catalysts supported on chemically reduced graphite oxide. The catalyst prepared by simultaneous reduction was the least active.

A Novel Synthesis of Gold Nanoparticles Supported on Hybrid Polymer/Metal Oxide as Catalysts for p-Chloronitrobenzene Hydrogenation

This contribution reports a novel preparation of gold nanoparticles on polymer/metal oxide hybrid materials (Au/P[VBTACl]-M metal: Al, Ti or Zr) and their use as heterogeneous catalysts in liquid phase hydrogenation of p-chloronitrobenzene. The support was prepared by in situ radical polymerization/sol gel process of (4-vinyl-benzyl)trimethylammonium chloride and 3-(trimethoxysilyl)propyl methacrylate in conjunction with metal-alkoxides as metal oxide precursors. The supported catalyst was prepared by an ion exchange process using chloroauric acid (HAuCl4) as gold precursor. The support provided the appropriate environment to induce the spontaneous reduction and deposition of gold nanoparticles. The hybrid material was characterized. TEM and DRUV-vis results indicated that the gold forms spherical metallic nanoparticles and that their mean diameter increases in the sequence, Au/P[VBTACl]-Zr > Au/P[VBTACl]-Al > Au/P[VBTACl]-Ti. The reactivity of the Au catalysts toward the p-CNB hydrogenation reaction is attributed to the different particle size distributions of gold nanoparticles in the hybrid supports. The kinetic pseudo-first-order constant values for the catalysts in the hydrogenation reaction increases in the order, Au/P[VBTACl]-Al > Au/P[VBTACl]-Zr > Au/P[VBTACl]-Ti. The selectivity for all the catalytic systems was greater than 99% toward the chloroaniline target product. Finally the catalyst supported on the hybrid with Al as metal oxide could be reused at least four times without loss in activity or selectivity for the hydrogenation of p-CNB in ethanol as solvent.

Improved catalytic performance of acid-activated sepiolite supported nickel and potassium bimetallic catalysts for liquid phase hydrogenation of 1,6-hexanedinitrile

Different inorganic acids were used to activate sepiolite, and the acid-activated sepiolites supported nickel and potassium bimetallic catalysts were prepared. Nitrogen adsorption-desorption, hydrogen chemisorption, ammonia temperature programmed desorption (NH3-TPD), temperature programmed reduction (TPR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and energy dispersive X-ray (EDX) were used to characterize the catalysts. The catalytic performance of the acid-activated sepiolite supported K-Ni bimetallic catalysts were investigated in 1,6-hexanedinitrile (HDN) hydrogenation in liquid phase. It was revealed that the potassium could increase the alkalinity of the catalyst with the aim of inhibiting the formation of the 1-azacycloheptane (ACH). And the addition of potassium reduces the particle size of nickel and improves its dispersion. Compared with hydrochloric acid and sulfuric acid, nitric acid treatment increases more silanol groups (SiOH) on the sepiolite surface, which is helpful to nickel particles adsorption and dispersion. Nitric acid activated sepiolite supported nickel and potassium bimetallic catalysts (K-Ni/NASEP) present the best catalytic performance, the conversion of HDN comes up to 92.0% under moderate conditions of lower temperature and pressure, the selectivity to 6-aminocapronitrile (ACN) and 1,6-hexanediamine (HDA) is up to 95.2%.

Pt-Al-TUD-1: A bifunctional catalyst for liquid phase hydrogenation of MIBK

A new heterogeneous catalyst contains two different catalytic sites is introduced. Pt-Al-TUD-1, which contains acidic and metallic active sites incorporated in a three dimensional mesoporous siliceous TUD-1 material, was prepared by one-pot synthesis procedure. Characterization data confirm the formation of metallic nanoparticles of Pt (5–10nm) incorporated on acidic Al-TUD-1 matrix. The catalytic performance of Pt-Al-TUD-1 was evaluated in the liquid phase hydrogenation of methyl isobutyl ketone (MIBK) at 453K. 13% conversion of MIBK was obtained after 4h with 99% selectivity towards 2-methylpentane (2-MP). The catalytic activity of the prepared catalyst outperformed the other metal incorporated Al-TUD-1 catalysts (metal=Pd, Ru, or Ag).

Physicochemical properties of palladium adsorbents as catalysts in liquid-phase hydrogenation

The structure and physicochemical properties of palladium catalysts used in liquid-phase hydrogenation processes were studied with the use of adsorption, calorimetric, thermogravimetry, and temperature-programmed reduction techniques. The specific surface areas and average sizes and volume of pores of the adsorbents were determined. The palladium on activated carbon catalysts was found to possess a complex porous structure, whereas palladium on combined alumina and coal carrier catalysts is an adsorbent with a nonporous structure. The concentration of the applied metal and the nature of a support have a significant impact on the physicochemical properties of palladium catalysts.

Highly selective catalysts for liquid-phase hydrogenation of substituted alkynes based on Pd—Cu bimetallic nanoparticles

Catalytic properties of Pd—Cu bimetallic catalysts supported on SiO2 and Al2O3 were studied in a model reaction of selective hydrogenation of diphenylacetylene. Application of PdCu2(AcO)6 heterobimetallic acetate complex as a precursor made it possible to obtain homogeneous Pd—Cu bimetallic nanoparticles. This result was supported by the data of IR spectroscopy of adsorbed CO. The Pd-Cu catalysts showed considerably higher selectivity than monometallic samples. Moreover, the introduction of copper decreases the hydrogenation rate of diphenylethylene (DPE) to diphenylethane. As a result, the maximum yield of the target product, DPE, increased from 78 to 93% in the presence of Pd—Cu catalysts.

A versatile bi-metallic copper–cobalt catalyst for liquid phase hydrogenation of furfural to 2-methylfuran

This work presents the application of bi-metallic copper–cobalt catalysts towards one step hydrogenation of furfural to 2-methylfuran in liquid phase.

Influence of niobium on carbon nanofibres based Cu/ZrO2 catalysts for liquid phase hydrogenation of CO2 to methanol

A series of carbon nanofibres supported Cu/ZrO2/Nb2O5 catalyst synthesized by deposition precipitation method were extensively investigated in relation to their performance in hydrogenation of CO2 to methanol. In order to study the promotion effect of niobium, catalysts were loaded with 0.4, 0.8 and 1.2wt.% of Nb2O5. Incorporation of Nb2O5 facilitated copper reduction by exhibiting a shift of highly reduced copper peak to lower temperature. Likewise, surface enrichment of copper was also enhanced by introduction of Nb2O5 to the catalysts. Activity studies of Nb2O5 doped Cu/ZrO2 catalysts were evaluated in a slurry reactor with a CO2/H2 gas mixture of 1:3 volume ratio, 180oC temperature and 3.0MPa total pressure. The highest activity was achieved with the incorporation of 0.8wt.% of Nb2O5, illustrating the high degree of CuO crystallization on the surface of catalyst are beneficial for the generation of copper catalyst with enhanced activities.

A recyclable Pd colloidal catalyst for liquid phase hydrogenation of α-pinene

A recyclable Pd colloidal catalyst was found to be effective for the liquid phase hydrogenation of α-pinene. Under optimal conditions, α-pinene conversion of 99.4% and cis-pinane selectivity of 81.3% were obtained. Furthermore, the Pd colloidal catalyst could be recovered conveniently and reused for eight runs without significant loss of the catalytic activity and selectivity.

Pt–Zn nanoparticles supported on porous polymeric matrix for selective 3-nitrostyrene hydrogenation

We report the promoting effect of Zn on performance of Pt-based catalyst in liquid-phase hydrogenation of 3-nitrostyrene (3-NS) to 3-vinylaniline (3-VA). Bimetallic Pt–Zn nanoparticles (NPs) were prepared within the hypercross-linked polystyrene (HPS) support. The nanoporous structure of HPS allows a size control of Pt–Zn NPs by confining them in the cavities (ca. 4–5nm) of the polymeric matrix. The TEM analysis showed that the mean size of the resulted metal particles (4.7nm) corresponds to the HPS pore size. The properties of the bimetallic catalyst were assessed by IR spectroscopy of chemisorbed CO that suggested the modification of Pt surface and electronic structure invoked by Zn incorporation. The catalytic results demonstrated an increased yield of 3-VA over Pt–Zn/HPS catalyst (97%) relative to monometallic Pt/HPS (16%). This is the highest result reported over Pt catalysts for NS hydrogenation without any additional reaction modifiers. Furthermore, stability of Pt–Zn/HPS under reaction conditions was confirmed over repeated reaction runs. Our results demonstrate the Pt modification with Zn as efficient means to control 3-VA selectivity, whereas HPS serves as a suitable support to control NP size and avoid metal leaching.

Stability of self-assembled monolayer coated Pt/Al2O3 catalysts for liquid phase hydrogenation

Thiolate self-assembled monolayers have recently been demonstrated to be effective catalyst modifiers for selectivity control, but these studies have not extensively explored the long term stability of these modifiers or the effects of specific reaction conditions. Here we investigate how the performance of thiolate-modified Pt/Al2O3 catalysts is affected by recycling and regeneration, using the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol as a probe reaction. Although modification of Pt catalysts with 3-phenyl-1-propanethiol results in high selectivity due to a ligand-specific interaction between modifier and reactant during the first use of a given catalyst, repeated recycling was shown to decrease the efficacy of this mechanism due to increasing disorder in the monolayer. However, selectivity and order could be stabilized using a thiol regeneration step or by feeding dilute concentrations of thiols in the reaction mixture. Similarly, aging in air was shown to decrease the order of the thiol and reduced the selectivity improvement of both a 3-phenyl-1-propanethiol and an octadecanethiol (C18) modified Pt/Al2O3 catalyst. These studies show that the ligand-specific interactions between the SAM and the reactant are particularly sensitive to conditions that can degrade the monolayer.

A Highly Efficient and Selective Nickel/Clay Catalyst for Liquid Phase Hydrogenation of Maleic Anhydride to Succinic Anhydride

Three Ni-based catalysts with different clay as support were prepared and tested in the hydrogenation of maleic anhydride, among which Ni/clay1 showed best activity and selectivity. Over Ni/clay1 catalyst prepared by impregnation method, 97.14% conversion of maleic anhydride and 99.55% selectivity to succinic anhydride were obtained at 180 .deg. C under a pressure of 1 MPa. Catalytic activity was greatly influenced by the temperature and weighted hourly space velocity. Catalyst deactivation studies showed that this catalyst have a long life time, the yield of MA still higher than 90% even after a reaction time of 60 h. X-ray diffraction (XRD) and H{sub 2} temperature programmed reduction (TPR) were use to investigate the properties of the catalyst. XRD and TPR studies showed that Ni was present as Ni{sup 2+} on the support, which indicated that there was no elemental nickel (Ni{sup 0}) and Ni{sub 2}O{sub 3} in the unreduced samples. The formation of Ni was strong impact on catalytic activity.

Study on deactivation of Ni/Al2O3 catalyst for liquid phase hydrogenation of crude 1,4-butanediol aqueous solution

The deactivation of a commercial Ni/Al2O3 catalyst in the liquid phase hydrogenation of crude 1,4-butanediol aqueous solution was investigated. A significant deactivation trend was observed during the operation time of 5000h. The fresh and deactivated catalysts were characterized by ICP-AES, N2 physisorption, H2-TPR, TEM, TPD, FTIR and XRD. The results indicate that, during the reaction process, the Al2O3 support transforms into its hydrate boehmite (γ-AlO(OH)), which further results in the aggregation of metal Ni, the decrease of BET specific surface area and the reduction of pore volume. The hydration of Al2O3 support is the main reason for the deactivation of Ni/Al2O3 catalyst. The promotion effect of SiO2 on the activity and stability of Ni/Al2O3 catalyst was also investigated. The results suggest that the introduction of SiO2 effectively inhibits the hydration of Al2O3 support and prevents the active decay of Ni/Al2O3 catalyst.

A Co-Promoted Ni-B Amorphous Nanoalloy Catalyst for Liquid Phase Hydrogenation of Furfural to Furfural Alcohol

The Co-promoted Ni-B amorphous nanoalloy catalysts were prepared by the chemical reduction of the aqueous solution containing nickel acetate and cobalt acetate with NaBH4 at room temperature and characterized by BET, XRD and DSC. They were used as catalysts for the liquid phase hydrogenation of furfural to furfural alcohol in alcohol at 353 K under 2.0 MPa of hydrogen. Ni-Co-B catalyst was characterized by XRD as amorphous structure. It was active in the hydrogenation of furfural, and it was significantly more active than Ni-B and Co-B. The optimal Co/ ( Co+Ni ) mole ratio in Ni-Co-B was 0.5.

Carbon nanofibers supported nickel catalyst for liquid phase hydrogenation of benzene with high activity and selectivity

Carbon nanofibers (CNFs) prepared by catalytic decomposition of ethylene are used as support for nickel. The CNF support displays a mean diameter of 50–60 nm, lengths up to several tens of micrometers, as highlighted by TEM. The nickel particles have a size distribution from 10 to 20 nm of diameter. This novel Ni/CNFs catalyst displays good catalytic properties in liquid phase hydrogenation of benzene at a reaction temperature of around 180 °C.