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Catalysts based on gold nanoclusters supported by different materials have been used for the selective semihydrogenation of phenylacetylene to styrene. The most active species were formed by catalyst thermal activation in a reductive atmosphere. It is shown that the activity and selectivity of these catalysts is mainly controlled by the interaction of the gold nanoclusters with the support, as demonstrated by using materials with high surface area and different acidity/basicity, i.e. MgO, Al 2 O 3 and Mg/Al hydrotalcite. There is an important influence of the acid/base properties of the support on the selectivity. Higher activity is obtained for gold supported on basic materials (MgO and hydrotalcite) and the best results are obtained with the Au catalyst supported on the MgAl hydrotalcite exhibiting high activity and the best selectivity to the alkene. This was explained by the intermediate basicity of the support that favors the heterolytic cleavage of H 2 while avoiding the overreduction of the alkynes to alkanes. [Display omitted] [ABSTRACT FROM AUTHOR]

Pd-based catalysts play an important role in selective hydrogenation reactions for the removal of polyunsaturated hydrocarbon traces (e.g. alkadienes) from alkene feedstocks. To improve the selectivity, Pd can be diluted with a more selective metal such as Cu, Ag or Au. We report a detailed study on the effect of the Pd:Cu ratio on the catalytic performance of carbon-supported Cu-rich catalysts for the selective hydrogenation of butadiene in an excess of propylene. Bimetallic Pd x Cu 100-x nanoparticles of 7–8 nm diameter with tuneable Pd content of 0.6–13 % were prepared colloidally. Catalytic turnover frequencies for butadiene hydrogenation increased with Pd-fraction up to 1.0 s−1 for Pd 7 Cu 93 and Pd 13 Cu 87. The butene selectivity, measured at 90 % conversion, was roughly 80 % for the catalysts with a Pd fraction above 3 % and slightly increased with lower Pd concentrations. Operando X-ray absorption spectroscopy identified an electron density transfer from Cu to Pd in the bimetallic catalysts and a slight preferential clustering of Pd. The trend in catalytic activity was ascribed to an increased Pd ensemble size, indicated by higher Pd-Pd coordination numbers. For bimetallic Pd x Cu 100-x /C catalysts, a Pd content of 3–7 % retains a high selectivity of 78 % at 90 % conversion, while improving the activity 3–4 orders of magnitude compared to pure Cu catalysts. These insights on how to control the activity-selectivity balance through metal nanoparticle compositions contributes to the rational design of bimetallic catalysts for selective hydrogenation reactions. [Display omitted] • Well-defined method for tuneable Pd-fraction in PdCu/C catalysts, keeping size and shape constant. • Co-existence of Cu and Pd within individual nanoparticles, with charge transfer from Cu to Pd. • Fraction-dependent activity, which increases with Pd-fraction, while selectivity remains similar. [ABSTRACT FROM AUTHOR]

The selective production of valuable 1,2-pentanediol (1,2-PeD) by biomass-derived furfural alcohol (FFA) hydrogenation is challenging due to the diverse unsaturated groups and robust C 5 –O bond. Here, a series of Pt/Mg x AlO y catalysts with tunable Mg/Al molar ratio were modified to adjust metal-support interactions and oxygen vacancy in promoting FFA hydrogenation in aqueous phase. Among them, Pt/Mg 7 AlO exhibited excellent catalytic performance, reaching almost complete conversion of FFA and the highest selectivity of 64.9% to 1,2-PeD. A combination study involving X-ray photoelectron spectroscopy (XPS), in situ CO diffuse reflectance Fourier transform infrared spectroscopy (CO-DRIFTS) and in situ FT-IR, confirms that the electrons-rich Pt0 species contribute to the significantly enhanced FFA hydrogenation via promoting C 5 –O bond cleavage. In-situ FT-IR experiments give direct evidence that the unique distorted adsorption mode of C 4 =C 5 –O groups in FFA induces high selectivity for targeted 1,2-PeD over Pt/Mg 7 AlO, while the parallel adsorption of furan ring is extremely suppressed. This study emphasizes the significance for optimizing defect sites of Mg x AlO y in rationally tuning Pt surface states for selective hydrogenation of biomass-derived furan compounds. [Display omitted] • Pt/Mg 7 AlO reached 64.6% yield of 1,2-PeD in FFA hydrogenation. • Pt/Mg 7 AlO's unique lamellar structure promotes Pt dispersion and PtO x reduction. • FFA is adsorbed and activated on the oxygen defect sites of Pt/Mg 7 AlO. • Electrons-rich Pt0 contributes to C 5 –O bond cleavage of FFA hydrogenation. [ABSTRACT FROM AUTHOR]

In spite of being commercialized for well over a century, hydrogenation is still a subject of intensive research and development. A patent landscape analysis showed high growth rates for topics related to climate change, bio-renewables, low waste and recyclability. The current paper describes trends, providing examples on the effect of structure sensitivity, on novel intermetallic active phases and on discoveries initiated by modelling. Due to increased processing costs and a negative environmental impact of undesirable by-products, the present focus favours high selectivity over activity. A relatively new class of materials showing an exponential growth in publications, these are the so-called intermetallics. These materials are defined as compounds formed by at least two metals, with – at least partly – ordered crystal structures which are different from the ones of the constituting elements. Non-metallic active phases formed by interaction of a metal ion and a (reducible) support may have a superior hydrogenation performance compared to the corresponding zero-valent metals. Aided by Density Functional Theory modelling (DFT) new, often intermetallic catalysts like Ni 5 Ga 3 were identified which sparked a great number of follow-up studies. • An exponential growth in hydrogenation patents in the last decade is observed. • For many reactions the rate of reaction declines when nanoparticle size decreases. • Non-metallic active phases may have a superior performance. • Aided by DFT, new catalysts like Ni 5 Ga 3 for CO 2 hydrogenation, were identified. [ABSTRACT FROM AUTHOR]

• A hybird nano-structure catalyst Pd/@-ZrO 2 /AC is prepared by photochemical route. • Synergistic effect between Pd nanoparticles and nano-semiconductor(ZrO 2)/AC. • Pd/@-ZrO 2 /AC shows excellent activity and high benzyl alcohol selectivity in the hydrogenation of benzaldehyde. • Pd/@-Me x O y /AC catalysts exhibited synergistic catalysis and remarkable catalytic activity. Selective hydrogenation of benzaldehyde is a green and sustainable technology to produce benzyl alcohol. Herein, we report a hybrid nano-structure catalyst(Pd/@-ZrO 2 /AC) by photochemical route for selective hydrogenation of benzaldehyde under mild reaction conditions. The Pd/@-ZrO 2 /AC catalyst exhibited outstanding activity(100%) and high selectivity for benzyl alcohol (>98 %), much higher than that of Pd/ZrO 2 and Pd/AC. The high catalytic activity was attributed to the special structure and the synergistic effect. A series of Pd/@-Me x O y /AC(Me x O y : TiO 2 , CeO 2 , La 2 O 3) catalysts further confirmed the synergistic effect in this hybrid nano-structure for this reaction. This work clearly demonstrates that loading nano-metal on high specific surface area materials with nano-semiconductors can increase the catalytic activity and open up a new direction for the synergistic catalysis of hybrid nano-structure catalysts. [ABSTRACT FROM AUTHOR]

• Pt/TiO 2 were synthesized by pulsed direct magnetron sputtering deposition. • Characteristics of Pt nanoparticles formed depended on deposition time. • Small Pt with high-coordinated surface could be obtained via pulsed DC-MSD. • Aqueous phase partial hydrogenation of vanillin was tested at 70 °C and 2 MPa. • Pt/TiO 2 prepared by pulsed DC-MSD was more effective than impregnation. Pulsed direct current magnetron sputtering (PDC-MSD) was employed for the deposition of Pt nanoparticles (ca. 0.1 wt.%) on anatase TiO 2 powder. According to the H 2 -TPR, XPS, and TEM-EDX results, the characteristics and properties of the deposited nanoparticles depended on the deposition time. During the initial deposition stage (45–90 sec), low-coordinated small spherical Pt nanoparticles were formed. Prolonging the deposition time (135–180 sec), led to the formation of larger Pt nanoparticles, which strongly interacted with the TiO 2. The catalytic activities of the prepared Pt/TiO 2 with different deposition times in the aqueous phase partial hydrogenation of vanillin to vanillyl alcohol ranged as follows: Pt/TiO 2 MSD-45 < Pt/TiO 2 MSD-90 < Pt/TiO 2 MSD-180 < Pt/TiO 2 MSD-135, which was in good agreement with the atomic Pt/Ti ratio and coordinated surface Pt atoms on the catalyst surface. The high catalytic activity of Pt/TiO 2 MSD-135 was attributed to the presence of well-dispersed small Pt nanoparticles with more highly-coordinated Pt surface atoms deposited on the TiO 2 anatase. PDC-MSD has been proven to be a more effective method for the preparation of supported metal catalysts, compared to those obtained by conventional impregnation technique. [ABSTRACT FROM AUTHOR]

• Porous aromatic frameworks stabilize palladium nanoparticles within their pores. • Amino-groups in aromatic frameworks contribute higher palladium dispersion. • Catalysts based on polymers with amino-groups convert selectively terminal alkynes. Palladium catalysts, based on porous aromatic frameworks, synthesized via Suzuki cross-coupling reaction and further modified with amino groups, were prepared and tested in hydrogenation of several unsaturated compounds. Catalysts obtained were characterized by several techniques including IR spectroscopy, solid-state NMR spectroscopy, low-temperature nitrogen adsorption, transmission electron microscopy, atomic emission spectroscopy and X-ray photoelectron spectroscopy. It was shown that the amino-groups within the structure of aromatic frameworks interact with palladium nanoparticles and enhance their selectivity towards hydrogenation of terminal alkynes. [ABSTRACT FROM AUTHOR]

• Pt nanocubes exposing {110} facets have been immobilized on few layer graphene. • The supported nanocubes are more active and more selective than the free nanocubes. • The outstanding activity is well correlated to size*Pt/ligand ratio. • The selectivity to cinnamyl alcohol is well correlated to the Pt/ligand ratio. • {110} facets allow higher activity selectivity as compared to {100} facets. Free and supported platinum concave nanocubes exposing {110} facets have been prepared by a wet-chemistry route and used as catalysts for the selective hydrogenation of cinnamaldehyde. The nanocubes were directly grown on few layer graphene support in the presence of octadecylamine as a stabilizing agent. Immobilization improves both activity and selectivity towards the desired unsaturated alcohol. The presence of the organic stabilizer guarantees the stability of the nanoparticle morphology and influences the catalyst performances. While the activity is favored by small nanoparticles and low ligand contents, the selectivity to the unsaturated alcohol is favored by high ligand contents, most likely due to steric effects that favor adsorption through the C=O moiety. Apart from stabilizing the nanocubes, the support interacts with the long chain amine ligand, behaving as a ligand reservoir. Thus, an equilibrium is established between the ligand interacting with the nanoparticles, the free ligand in solution, and the ligand interacting with the support. Ligand redistribution during the catalytic reaction assures a good compromise between activity and selectivity even after three recycling tests. While a direct comparison with other catalysts is not straightforward, the FLG-supported concave nanocubes presented outstanding activity, and selectivity to cinnamyl alcohol higher than 80%. [ABSTRACT FROM AUTHOR]

• Well defined Co-CoO@SiO 2 core-shell structures were fully synthesized. • Co-CoO@SiO 2 catalysts show hydrogenation catalytic performance. • An optimum Co/CoO ratio produces highest selectivity towards unsaturated alcohol. • No cobalt leaching in Co-CoO@SiO 2 reduced at500 °C catalyst was observed. The effect of the reduction temperature (300 °C, 400 °C, 500 °C and 600 °C) in cobalt SiO 2 core-shell catalysts for chemoselective hydrogenation of cinnamaldehyde is reported. The Co-CoO@SiO 2 catalysts structures were synthesized starting from a calcined Co 3 O 4 @SiO 2 nanostructure obtained using a solvothermal method for the core (Co 3 O 4) and a modified Stöber method for the porous shell (SiO 2) submitted to different reduction temperatures. The initial Co 3 O 4 @SiO 2 structure and the derived Co-CoO@SiO 2 catalysts were characterized by AAS, TG/DTG, TPR, TEM, XRD, XPS and S BET. The increase in the metallic Co content along with the reduction temperature increased the total conversion of cinnamaldehyde in the liquid-phase hydrogenation reaction. The highest selectivity towards the unsaturated alcohol over Co-CoO@SiO 2 -500 °C catalyst was attributed to an optimum Co/CoO surface ratio. A large chemical and mechanical stability of the Co-CoO@SiO 2 structure was evidenced after five consecutive reaction cycles, revealing the beneficial effect of the core-shell architecture towards cobalt leaching in liquid-phase reactions. [ABSTRACT FROM AUTHOR]

Selective hydrogenation of a trace amount of acetylene to ethylene is a green and economical process to purify the ethylene stream in the olefin industry. Pd-based catalysts are widely explored for this process due to their excellent H 2 and C 2 H 2 activation abilities. However, the strong adsorption of C 2 H 4 on metallic Pd sites often leads to the undesired over-hydrogenation product (i.e., ethane). Herein, we fabricated Pd/MgAl 2 O 4 catalysts with tunable metal-support interactions by changing calcination temperatures to efficiently modify the electronic structure of Pd species. The Pd/MgAl 2 O 4 with the optimized calcination temperature exhibits 96 % acetylene conversion and enhanced ethylene selectivity of 87 % due to weak adsorption of intermediates at 120 ℃, and shows excellent stability with negligible activity decay during a 50 h test. This work provides a strategy for designing catalysts with regulated metal-support interactions for selective hydrogenation processes. [Display omitted] • Pd/MgA1 2 O 4 catalysts with tunable metal-support interactions are developed. • The electronic structure and catalytic properties of Pd sites can be regulated. • The optimized metal-support interactions lead to the formation of Pdδ+ species. • Pdδ+ species bind intermediates weakly and then exhibit enhanced selectivity. [ABSTRACT FROM AUTHOR]

This work studies the catalytic properties of Cu and Ni catalysts, as well as the effect of Cu and Ni combination on the activity and selectivity during the aqueous phase hydrogenation of 5-hydroxymethylfurfural (HMF) in a batch reactor, at 60 °C under 30 bar H 2. Catalysts with different Ni/Cu ratios (10 wt%) were synthesized over a high surface area graphite (HSAG). While Ni provides the bimetallic catalyst the capacity for hydrogenation of C O and C C groups, Cu contributes to suppress the hydrogenation of the furan ring, reaching a 99% of selectivity to the partial hydrogenated product, 2,5-di-hydroxymethylfuran (DHMF), over 5Cu5Ni/HSAG. The increase of reaction temperature (180 °C) conduced to the hydrolytic ring-opening and rearrangement of HMF. Under such reaction conditions, monometallic Ni afforded the highest yield towards the hydrogenative rearrangement product, 3-hydroxymethylcyclopentanone (81%). However, Cu and CuNi bimetallic catalysts were less reactive to the ring-rearrangement reaction and showed higher tendency to deactivation, especially when the HMF supplier contain sulfur impurities. [Display omitted] • There is a synergic effect between Cu and Ni in the partial hydrogenation of 5-hydroxymethylfurfural. • Cu suppresses the C C hydrogenation ability of Ni in favor of the carbonyl hydrogenation product. • Cu and Ni are effective in the ring-opening and rearrangement reactions under additive-free conditions. • The reagent purity influences on the kinetics, products yields and catalyst's recyclability. • Sulfur impurities of the feedstock affect more severely to Cu than Ni catalysts. [ABSTRACT FROM AUTHOR]

• Melt infiltration is efficient for the dispersion of nickel in micro-mesoporous silica. • Properties of the secondary intra-wall porosity is decisive in dispersing Ni phase. • A high degree of interconnectivity between the two porosities is in favor of NPs formation in the intra-wall pores. • Excellent properties for cinnamaldehyde and 5-HMF hydrogenations are obtained over intra-wall pore confined NPs. Effective encapsulation strategies are highly sought-after in heterogeneous catalysis for preparing highly active and stable metal (oxide) nanocatalysts. Herein, we report an optimized Melt Infiltration (MI) procedure to confine nickel(oxide) nanoparticles (NPs) into hierarchical microporous-mesoporous scaffolds. Three SBA-15 silicas were synthesized in order to obtain different degrees of interconnectivity between the main mesopores. The impact of the SBA-15 pore characteristics, i.e. , this interconnectivity, also named secondary intra-wall porosity (IWP), on the final nickel (oxide) NPs size and localization has been specifically investigated. Using MI, which consisted in the diffusion of the precursor in the liquid state inside the porosity of the support in the presence of the native surfactant occluding the pores, a selective localization of the NiO NPs inside the IWP was obtained, without large NPs plugging the main mesopores if IWP pores connecting the main mesopores do exist. When IWP – selective localization – occurs for the NPs, they show a size directly depending on the IWP dimensions. The obtained materials were tested, after reduction, in the hydrogenation reactions of cinnamaldehyde and 5 -hydroxymethylfurfural. The catalytic results underline the positive effect of IWP - confinement of NPs to obtain and maintain an elevated dispersion of the metallic Ni active phase and to reach a high catalytic activity in hydrogenation under mild reaction conditions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Introduction to intermetallics as model catalysts for important chemistries. • Review of intermetallic nano-crystal synthesis methods and current challenges. • Discussion on proper characterization of the catalytic multi-metallic surface. • Review of applications of intermetallic catalysts and advantage over pure metals. Abstract In this article, we highlight the growing application of intermetallic compounds in heterogeneous catalysis. We clearly discuss intermetallics as distinct from other multi-metallic systems (such as alloys, surface modifiers and dopants). Intermetallics possess a number of attributes over random alloys (i.e., solid solutions) and serve as model catalysts for a number of industrially relevant reactions. We review a variety of methods used for the synthesis of a large number of intermetallic compounds and discuss how standard material characterization techniques can be extended to intermetallics to gain important insight regarding active site morphology, a critical metric in heterogeneous catalyst design. We further summarize the use of intermetallics in understanding changes in reactivity and selectivity due to geometric and electronic effects, with emphasis on determining compositional and structural factors of the active site. We conclude with a brief summary of avenues for future advances in the field and its potential to contribute to environment and economy. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Catalyst support effect has been studied for 2(5H)-furanone hydrogenation to GBL. • Pt-Ni and Pt catalysts are compared over SiO 2 , Al 2 O 3 , TiO 2 , ZrO 2 and TiO 2 -ZrO 2. • Bimetallic effect is observed over all five oxide supports. • Pt-Ni/SiO 2 is the most promising catalyst for 2(5H)-furanone hydrogenation to GBL. Abstract Our previous work has identified the Pt-Ni/SiO 2 bimetallic catalyst as a promising catalyst for the selective hydrogenation of biomass-derived 2(5H)-furanone to γ-butyrolactone (GBL). The competitive relationship between the selective hydrogenation of 2(5H)-furanone over Pt-Ni metal sites and the polymerization side reactions over the oxide support is found to be a key factor for the production of GBL. The current work investigates the effect of oxide supports on the selective hydrogenation of 2(5H)-furanone by comparing Pt-Ni bimetallic and Pt monometallic catalysts supported on SiO 2 , Al 2 O 3 , TiO 2 , ZrO 2 and TiO 2 -ZrO 2. A synergetic bimetallic effect was observed over all five oxide supports, as the Pt-Ni bimetallic catalyst is more selective and active toward the production of GBL than the corresponding Pt monometallic catalyst. Catalysts on the non-acidic and non-reducible SiO 2 showed a better catalyst performance than those on either the acidic Al 2 O 3 with a high surface area or the partially reducible TiO 2 , ZrO 2 and TiO 2 -ZrO 2 with relatively low surface areas and different acid sites. The performance of the five Pt-Ni bimetallic catalysts follows the trend of SiO 2 > Al 2 O 3 > TiO 2 > TiO 2 -ZrO 2 > ZrO 2 based on the GBL yield. The GBL yield was further improved by using the SiO 2 support with a higher surface area and increasing the metal loadings of Pt and Ni to increase the number of hydrogenation active sites. [ABSTRACT FROM AUTHOR]

Bimetallic SnPt-nanoparticle (SnPt-NP) catalysts with several types of Sn x Pt y alloy structures were prepared using a polyalcohol reduction process; the catalytic behavior of each Sn x Pt y alloy phase toward the selective hydrogenation of unsaturated aldehydes to the corresponding unsaturated alcohols was elucidated. Atomic absorption spectroscopy (AAS) and transmission electron microscopy (TEM) indicate that SnPt-NP catalysts with various Sn/Pt atomic ratios can be successfully prepared by a polyalcohol reduction process using Pt(acac) 2 and Sn(AcO) 2 as the metal precursors. X-ray diffraction (XRD) results reveal that the Sn 1 Pt 3 , Sn 1 Pt 1 , and Sn 2 Pt 1 alloy phases are formed through control of the Sn/Pt atomic ratio of the starting mixture during preparation. The Sn 1 Pt 3 alloy phase enhanced the hydrogenation of both the C C and C O bonds during the selective hydrogenation of crotonaldehyde. When only Sn 1 Pt 1 alloy phases (Sn/Pt = 1.40), accompanying with separated Sn phase, were formed in the SnPt-NP catalysts, the highest unsaturated alcohol (UOL) selectivity (71.5% at 37.6% conversion) was observed. The formation of the Sn 2 Pt 1 alloy phase led to decreased UOL selectivity. We suggest that the Sn 1 Pt 1 alloy phase is an effective bimetallic SnPt hydrogenation catalyst for the selective formation of unsaturated alcohols. [ABSTRACT FROM AUTHOR]

Heterogeneous selective hydrogenation plays an important role in the manufacture of high value-added chemicals. Modification of noble metal catalysts, e.g. Pd, Pt and Au, by using inorganic or organic compounds has been emerging as one of the most effective strategies to enhance the substrate selectivity, chemoselectivity, and enantioselectivity as well. The purpose of this paper is to review recent experimental and theoretical advances on this topic. We will concentrate on the steric and/or electronic effects at the surface/interface induced by the surface molecular modifiers, and how these effects work alone or together to generate a high selectivity. [ABSTRACT FROM AUTHOR]

A range of oxides (γ-Al 2 O 3 , TiO 2 , ZrO 2 , CeO 2 , α-Fe 2 O 3 and Fe 3 O 4 ) with different redox properties were used to support nano-scale (mean = 2–8 nm) Au and employed in the gas phase hydrogenation of benzaldehyde and nitrobenzene. The catalysts were subjected to TPR, H 2 /O 2 titration, H 2 TPD, XRD, TEM/STEM and XPS analysis. The supported Au phase promoted partial reduction of the reducible supports through the action of spillover hydrogen (based on TPD), which generated surface oxygen vacancies (demonstrated by O 2 titration) that inhibit Au particle sintering during catalyst activation. Electron transfer to generate charged Au species (determined by XPS) correlates with support ionisation potential. Higher nitrobenzene hydrogenation (to aniline) TOF s were recorded relative to benzaldehyde where rate increased with decreasing Au size (from 8 to 4 nm) with measurably lower TOF over Au <3 nm. Strong binding of CH O and NO 2 functions to oxygen vacancies resulted in lower hydrogenation rates. Higher temperatures (>413 K) promoted benzaldehyde hydrogenolysis to toluene and benzene. The formation of Au δ− on non-reducible Al 2 O 3 favoured selective reduction of CH O with full selectivity to benzyl alcohol at 413 K. [ABSTRACT FROM AUTHOR]

Heterogeneous palladium catalysts with high atom-efficiency offer practical value for selective hydrogenation. Here, we prepared atomically dispersed Pd species supported on γ-AlOOH nanosheets (Pd/γ-AlOOH), which contain clusters and dominated single atoms. Even with an extremely low amount of Pd loading, the catalytic activity of 0.1Pd/γ-AlOOH leads to 50.3% of succinic acid conversion at 4 h. At the time, the succinic acid conversion reaches 90.7% and 97.1%, and the selectivity to γ-butyrolactone is high up to 96.9% and 93.8% over 0.5Pd/γ-AlOOH and 1.0Pd/γ-AlOOH, respectively. The supported Pd single atom (Pd 1 /γ-AlOOH) Exhibits 30- and 1100-fold increase in the catalytic activity compared with the supported clusters Pd 13 /γ-AlOOH and Pd 55 /γ-AlOOH for the selective hydrogenation of succinic acid to γ-butyrolactone, respectively. Analysis of the structural properties confirms that Pd single atoms on γ-AlOOH (0 1 0) surface have high adsorption energy, which is in agreement with catalytic efficiency. In addition, Pd single atoms in the catalyst 0.2Pd/γ-AlOOH account for 86.6% of the overall catalytic activity and can serve as the most efficient catalytic active sites. [ABSTRACT FROM AUTHOR]

We report herein on the development of Ni-based catalyst using activated carbon fibres (ACFs) as a structured support and its application for the three‐phase hydrogenation of nitroarenes ( T = 353 K; P = 10 bar). It was shown that metallic Ni 0 nanoparticles (NPs) with a mean diameter of ∼2.0 nm stabilized by the ACF microporous network were responsible for the catalytic transformation. To obtain optimum catalytic activity, the Ni/ACF catalyst must be freshly prepared and activated in situ by H 2 at T > 353 K. Pre-treatment of the ACFs by nitric acid boosted the activity of the Ni/ACF catalyst, which exhibits high performance in hydrogenation of nitrobenzene to aniline (yield, Y ∼100%). The catalyst was tested for the reuse attaining a quasi-steady-state after the sixth reaction thereafter remaining relatively stable over seven consecutive runs. Near-quantitative transformation (Y > 99%) of p- chloronitrobenzene to p‐ chloroaniline was achieved under mild conditions over the Ni/ACF catalyst with a ca . 20-fold higher activity than conventional Raney Ni. Thus, new catalyst reported here represents a significant step forward towards a simple, heterogeneous catalytic selective hydrogenation of nitroarenes that employs H 2 as the hydrogen source. [ABSTRACT FROM AUTHOR]

Bimetallic Pd–Cu/Al 2 O 3 and Pd–Zn/Al 2 O 3 catalysts with various Cu/Pd and Zn/Pd molar ratios were prepared and applied to the selective hydrogenation of phenylacetylene to styrene. The structure properties of the bimetallic catalysts were characterized by inductively coupled plasma–optical emission spectroscopy (ICP–OES), CO chemisorption, high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). Different from Pd–Cu/Al 2 O 3 where the interaction between Pd and Cu only generated the geometric effect, both geometric and electronic effects were observed for Pd–Zn/Al 2 O 3 . The activity and selectivity of the bimetallic catalysts can be tuned by varying the Cu/Pd and Zn/Pd molar ratios, which were essentially determined by the geometric and electronic effects of the catalysts. Although both Pd–Cu/Al 2 O 3 and Pd–Zn/Al 2 O 3 exhibited improved selectivity to styrene compared to monometallic Pd/Al 2 O 3 , there is a difference in the activity and selectivity between the two types of bimetallic catalysts at the same Cu/Pd and Zn/Pd molar ratio, which is mainly caused by the different modification degrees of Cu and Zn on Pd. Among all the catalysts prepared in this work, the Pd–Zn/Al 2 O 3 with a Zn/Pd molar ratio of 6 displayed the best selectivity to styrene, being 86.3% at 99.5% phenylacetylene conversion. [ABSTRACT FROM AUTHOR]

Restructuration of AuPd/CeO 2 catalysts is observed during 1,5-cyclooctadiene hydrogenation, with gold surface segregation in which gold acts as a diluent of Pd surface sites. The composition of the catalyst influences the catalytic behavior, and an optimum is observed at a Pd/Au molar ratio of 0.13, as determined by X-EDS STEM. Pd–Au/CeO 2 shows higher hydrogenation rates (11.2 × 10 −5 mol/g s) versus the unpromoted Pd/CeO 2 catalysts (1.7 × 10 −5 mol/g s), and the Pd/TiO 2 (7.5 × 10 −5 mol/g s) catalysts used as conventional hydrogenation catalysts. Since the active sites are generated under reaction conditions, characterization of the catalysts after quenching the reaction at specific reaction times was required. [ABSTRACT FROM AUTHOR]

The waste stream containing high vinyl acetylene concentration from a commercial mixed C4 process was tested for the hydrogenation reaction by Pd, Mn-Pd, Ni-Pd, and Ag-Pd supported on alumina catalysts in a recirculating reactor. Mn-promoted Pd/Al 2 O 3 catalyst with Pd/Mn molar ratio 1:2 not only increases the activity, but also significantly increases the selectivity and yield toward 1,3-butadiene. Adding Ni to Pd/Al 2 O 3 catalysts improves only the activity, but not the selectivity, while adding Ag improves neither the activity nor the selectivity toward 1,3-butadiene. [ABSTRACT FROM AUTHOR]

Selective hydrogenation of acetylene is usually a gas-phase reaction. In this work, liquid phase was introduced as a selective solvent to improve the selectivity to ethylene by coupling absorption to the reaction. N -methyl-2-pyrrolidone (NMP) and 1,3-dimethylimidazolium methylphosphite ([DMIM][MeHPO 3 ]) were used as selective solvents in two types of liquid modification (in bulk liquid phase and on SCILL). Both types of modification significantly enhanced the ethylene selectivity compared with the gas-phase reaction. The mass transfer could be eliminated almost completely in bulk NMP, slightly on SCILL, but could not be eliminated in bulk [DMIM][MeHPO 3 ]. Among the reactions with liquid introduction, the reaction in bulk NMP could increase the ethylene selectivity to the greatest extent, which had a highest ethylene selectivity of 96.6% at conversion of 96.1%, and outperformed SCILL in catalyst stability. [ABSTRACT FROM AUTHOR]

Transition metals such as Fe and Ni are the most commonly used catalysts for the growth of carbon nanofibers (CNFs) via CCVD method, and they always remain in the raw products. Much attention has been paid to purify CNFs, i.e., to remove residual metal particles and supports, before their use in most cases. However, some recent studies show that the residual metal particles usually attach at the tips of CNFs, and exhibit a different shape in comparison with the initial metal catalysts and as a result unique catalytic performance. The present review focuses on the state-of-the-art of the developments of synthesis of reshaped Fe and Ni particles at the tips of CNFs and their catalytic applications in cellulose conversion, selective hydrogenation and ammonia decomposition. In particular, effects of catalyst support, carbon source and its concentration, reaction temperature and etching gas are discussed. Moreover, the carbon adsorbates induced effect is highlighted as one of the key factors governing the reshaping of Fe and Ni particles. [ABSTRACT FROM AUTHOR]

The features of multiphase reaction media using water (bulk water, supported thin aqueous phase) and dense phase carbon dioxide are reviewed for selective hydrogenation of carbonyl, nitro, and cyano compounds. The interface of aqueous and organic phases is important in determining the rate of hydrogenation and the product selectivity. For supported aqueous phase catalysts, the interface between the thin aqueous film and a support material (for example, porous silica gel) has also an influential impact. The pressurization of a liquid reaction mixture (organic and/or aqueous phases) with carbon dioxide shows interesting positive effects on the reaction rate, the product selectivity, and the deactivation of a conventional supported metal catalyst. In some cases the use of both water and dense phase carbon dioxide serves as an effective reaction medium. In other words, these green solvents may act as reaction promoters. Possible roles of their actions are discussed. [ABSTRACT FROM AUTHOR]

This work reports the use of ionic liquids (ILs) as solvent for the synthesis of Au/TiO2 heterogeneous catalysts. It is shown that the versatility of the physico-chemical properties of ILs makes them interesting solvents for a broad control of supported metal nanoparticles (NPs) size and for a fine-tuning of metal-support interaction. Synthesis and deposition of Au NPs on TiO2 are carried out through a colloidal route in imidazolium-based ILs (1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) and trifluoromethanesulfonate (BMIMOTf)) and in a Deep Eutectic Solvent (DES, choline chloride and urea). The stabilization of the dispersed NPs and their deposition on an oxide carrier is investigated in pure ILs and in the presence of extra stabilizing agents (1-methylimidazole or polyvinylpyrrolidone). In the absence of TiO2, the NPs stability varies with the composition of the IL (BMIMOTf > BMIMPF6 > DES) and is critically depending on the addition of an extra stabilizing agent (SA). Conversely, when gold NPs are synthesized in the presence of TiO2 in imidazolium ILs, the addition of a SA is no longer required since the oxide support acts as a stabilizer for the gold colloids and prevents aggregation of NPs. A detailed XPS investigation of the surface composition of the TiO2-supported gold catalysts shows that the cationic part of the imidazolium ILs on the one hand and urea in DES on the other hand are co-adsorbed with gold NPs upon deposition on TiO2, probably decorating and stabilizing the Au NPs. The fate of the anionic part of the ILs (PF6-, OTf- and Cl-) is highly depending on the type of IL. Limited surface adsorption is reported for triflate (BMIMOTf) and chloride anions (DES), the latter being fully removed upon calcination, while PF6- (BMIMPF6) remains adsorbed on the surface during Au NPs deposition and leads to POxδ- and F- surface species upon calcination. The surface composition controls the intrinsic catalytic activity (TOF) in the selective hydrogenation of butadiene. It is shown that the surface doping of supported Au NPs with P and F anionic deposits (synthesized in BMIMPF6) has a promoting effect for the intrinsic catalytic activity. [ABSTRACT FROM AUTHOR]

Highlights: [•] Monolithic catalysts prepared by coating porous hollow nano-catalysts on substrate. [•] The new catalyst kept the excellent catalytic performance from the nano-washcoat. [•] The new catalyst showed high selectivity for selective hydrogenation of acetylene. [•] Adding a proper amount of Ag further enhanced the catalytic performance. [ABSTRACT FROM AUTHOR]

Highlights: [•] Selective hydrogenation of methyl oleate to oleyl alcohol on Ru–Ge–B/Al2O3 catalysts was studied. [•] Ge is deposited both over Ru metal sites and over the support. [•] Ge deposited on the metal function is in strong interaction with Ru. [•] Increasing the Ge content produced a decrease of the hydrogenation activity. [•] The Ge/Ru=2 is the optimum ratio to higher oleyl alcohol production. [Copyright &y& Elsevier]

Highlights: [•] Pd/IL/SiO2 catalysts are effective for selective hydrogenation of acetylene in ethylene. [•] RF non-thermal plasma was first applied to the Pd/IL/SiO2 for selective hydrogenation of acetylene. [•] Catalysts with ionic liquids of [BF4] anion are more active than those with [PF6] anion. [•] Pd/EmimBF4/SiO2 with Ar plasma+H2 procedure is more stable than the one with the conventional reduction. [Copyright &y& Elsevier]

Abstract: Several magnesia and zirconia systems were synthesized through the sol–gel process (calcination temperature in the 175–600°C range) and tested for liquid and gas-phase Meerwein–Ponndorf–Verley reduction of crotonaldehyde with 2-propanol. In the liquid phase, only zirconia systems were active, probably because carbonates and water “poison” active sites in basic magnesia. Moreover, the more surface OH groups were present in zirconia solids, the higher the activity exhibited. As far as reactions in the gas phase are concerned, both zirconia and magnesia solids were active, the latter exhibiting higher conversions at the same reaction temperatures. Furthermore, for MgO solids selectivity to crotyl alcohol increases with the reaction temperature which suggests that either new active sites were “in situ” created or the existing ones were unblocked and made accessible to the reactants. All in all, selectivities to crotyl alcohol of ca. 62% at 16% conversion were obtained for more active systems ZrO2-200 and ZrO2-250 in the liquid phase whereas values above 85% at 50% conversion were achieved on MgO solids in the gas-phase. [Copyright &y& Elsevier]

Abstract: A tetragonal molybdenum nitride (β-Mo2N) has been prepared by temperature programmed treatment of MoO3 in flowing N2 +H2 and for the first time shown to catalyze the liquid phase selective hydrogenation (T =423K; ) of a series of para-substituted (–H, –OH, –O–CH3, –CH3, –Cl, –I and –NO2) nitrobenzenes to give the corresponding aromatic amine. Reaction over Pd/Al2O3, as a benchmark catalyst (Pd particle size ca. 18nm), resulted in a composite hydrodechlorination/hydrogenation of p-chloronitrobenzene (as a representative nitroarene) to generate nitrobenzene and aniline. β-Mo2N has been characterized in terms of temperature-programmed reduction (TPR), H2 chemisorption/temperature programmed desorption (TPD), BET surface area/pore volume, elemental analysis, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning (SEM) and transmission (TEM) electronic microscopy. Elemental analysis, XRD, SEM and TEM have confirmed the formation of tetragonal β-Mo2N, characterized by an agglomeration of flake-like crystallites. Post-synthesis, the nitride was passivated by contact with 1% (v/v) O2/He at ambient temperature and XPS analysis has demonstrated the formation of a superficial passivating oxide overlayer without bulk oxidation. Pre-reaction, activation by TPR to 673K was necessary to remove the passivating film. Hydrogen TPD has revealed significant hydrogen uptake (0.7μmolm−2) associated with β-Mo2N. Nitro group reduction kinetics have been subjected to a Hammett treatment where the reaction constant (p =0 4) is diagnostic of an increase in rate due to the presence of electron-withdrawing substituents on the aromatic ring, consistent with a nucleophilic mechanism. The results presented in this study establish the viability of β-Mo2N to promote selective nitroarene hydrogenation. [Copyright &y& Elsevier]

Abstract: Microkinetic model is developed in the free energy landscape based on density functional theory (DFT) to quantitatively investigate the reaction mechanism of chemoselective partial hydrogenation of crotonaldehyde to crotyl alcohol over Pt(111) at the temperature of 353K. Three different methods (mobile, immobile and collision theory models) were carried out to obtain free energy barrier of adsorption/desorption processes. The results from mobile and collision theory models are similar. The calculated TOFs from both models are close to the experiment value. However, for the immobile model, in which the free energy barrier of desorption approaches the energy barrier, the calculated TOF is 2 orders of magnitude lower than the other models. The difficulty of adsorption/desorption may be overestimated in the immobile model. In addition, detailed analyses show that for the surface hydrogenation elementary steps, the entropy and internal energy effects are small under the reaction condition, while the zero-point-energy (ZPE) correction is significant, especially for the multi-step hydrogenation reaction. The total energy with the ZPE correction approaches to the full free energy calculation for the surface reaction under the reaction condition. [Copyright &y& Elsevier]

Abstract: Trans-stilbene (trans-ST) was produced through the hydrogenation of diphenylacetylene (DPA). Pd-based intermetallic compounds (IMCs) supported on silica were applied to the selective hydrogenation of DPA into cis- and trans-ST. Pd3Bi/SiO2 showed the highest selectivity to stilbenes without accelerating the deep hydrogenation into diphenylethane (DPE), after DPA was completely converted. Proton-type zeolites were examined for the isomerization of cis-ST, the main product in the hydrogenation of DPA, into trans-ST. H-USY zeolite partially exchanged with Na+ ions gave the highest activity owing to the appropriate acid strength and enough space inside the pores for cis-ST to enter. The mixture of Pd3Bi/SiO2 and H-USY gave trans-ST yield of 74mol% through the one-pot reaction of DPA. The isomerization rate was significantly retarded by coexisting DPA and DPE molecules. [Copyright &y& Elsevier]

Abstract: A series of Pd catalysts supported on various silicas including mesoporous silica and non-porous silica was prepared in order to elucidate activity controlling factors for the selective hydrogenation of 1-nitrohexane to N-hexyl hydroxylamine ( n Hex-NHOH). The Pd on silica (5wt.%) catalysts were characterized by XRD, N2 adsorption/desorption, and CO chemisorption. The hydrogenation was done in isopropyl alcohol under 1bar of H2 at room temperature. The Pd catalysts supported on non-porous silica or silicas that possessed large pores efficiently produced n Hex-NHOH in high yields, presumably because the influence of pore diffusion was small. Additionally, the catalytic activity strongly depended on the Pd dispersion: the activity generally decreased with the increased Pd dispersion (or the decreased Pd particle size). On the other hand, the yield of n Hex-NHOH was little affected by the initial oxidation state of surface Pd before hydrogenation. [Copyright &y& Elsevier]

Abstract: Carbon xerogels are mesoporous materials obtained upon pyrolysis of the dried gels resulting from polycondensation of resorcinol and formaldehyde. Treatment with nitric acid under severe conditions introduces high amounts of oxygen containing functional groups onto the surface of the material, leading however to the collapse of its porous structure. The resulting material is then used to support 1wt.% Pt, Ir and Ru monometallic catalysts by wet impregnation using organometallic precursors. The catalysts are characterized by N2 adsorption–desorption isotherms at 77K, temperature programmed desorption coupled with mass spectrometry, scanning and transmission electron microscopy, and H2 chemisorption. The liquid-phase selective hydrogenation of cinnamaldehyde to cinnamyl alcohol is used in order to assess the catalytic performance of the prepared materials. Pt and Ru catalysts are initially very selective towards the hydrogenation of the olefinic double bond, while Ir is mostly selective towards the carbonyl group. After a thermal post-reduction treatment at 973K, selectivity towards cinnamyl alcohol is significantly improved regardless of the metal nature. The Pt catalyst exhibits the best behavior, a complete shift in C=C to C=O hydrogenation being detected. The improvement in selectivity is rationalized in terms of both an increase in metal particle size and a modification in the surface chemistry of the catalyst after the post-reduction treatment. [Copyright &y& Elsevier]

Abstract: An attempt has been made at obtaining a catalyst for hydrogenation of ortho-chloronitrobenzene (o-CNB) to ortho-chloroaniline (o-CAN) which would be both selective and active. Ruthenium has been used as the active phase since it is the most selective of all metals investigated in the above reaction. Catalyst precursors, RuCl3·3H2O and NH4VO3, were introduced onto an unconventional support – MgF2 and reduced in hydrogen flow at 673K. The catalysts obtained revealed unusually high activity and selectivity in the reaction of hydrogenation of o-CNB to o-CAN, both in the gas- and liquid phase. The structural study of the Ru-V/MgF2 catalyst has shown that its high activity and selectivity were determined by the strong metal–support interactions and ruthenium–VO x species electron interactions. [Copyright &y& Elsevier]

Abstract: The introduction of foreign elements inside the channel of carbon nanotubes could lead to a significant modification of the intrinsic properties of these nanomaterials. Nitrogen atoms entering in the graphene sheets as substitute of carbon could modify in a large extend the acido-basic properties and also adsorption of the nanotube itself. Depending on the synthesis conditions, i.e. nature of the N-source, temperature and C-to-N atomic ratio, various N-doped carbon nanotubes can be synthesized with different surface properties. The aim of the present work is to report the synthesis of N-doped CNTs using a common nitrogen source precursor namely ammonia (NH3) with C2H6 as carbon source. The as-synthesized N-CNTs were subsequently employed as catalyst support in the liquid-phase hydrogenation of cinnamaldehyde using palladium as an active phase. [Copyright &y& Elsevier]

Abstract: Catalysts based on gold are now well established as very active and selective for broad ranges of redox reactions. Although primarily known for selective and preferential oxidation reactions, gold catalysts are also highly effective for selective hydrogenation. Hydrogenation reactions provide the focus for this perspective paper that is based on a François Gault lecture given at the Sabatier Conference in 2007. In particular, two reactions will be discussed; namely, the use of supported gold catalysts for selective hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols, and the use of supported gold palladium alloys for the direct hydrogenation of molecular oxygen to form hydrogen peroxide in preference to water. [Copyright &y& Elsevier]

Abstract: Au/Nb2O5 and Au/CeO2 catalysts were studied for the selective hydrogenation of crotonaldehyde, both in liquid (batch reactor, 4atm, 60°C, solvent: isopropanol) and in gas (flow microreactor, 120°C, atmospheric pressure) phases. Samples were characterized by TPR and XRD and tested for the CO oxidation reaction. Large differences in support reducibility between both catalysts were determined from the TPR results. The XRD and CO oxidation results demonstrated that the gold particles were lower than 5nm. The dependence of the selectivity towards crotyl alcohol and of the conversion on time on stream was measured. The niobia-supported catalyst was mainly unselective, the selectivity towards crotyl alcohol value being 20% for both liquid and gas phases. The Au/CeO2 catalyst is highly selective in gas phase (78% of selectivity towards crotyl alcohol). Under liquid phase conditions, a high selectivity level was not reached mainly due to secondary reactions. [Copyright &y& Elsevier]

Abstract: Three different carbon-based monoliths are studied in their performance as Pd-catalyst supports in the selective hydrogenation of fatty acid methyl esters of sunflower oil (FAME). The first monolithic support (HPM) was a classical square channel cordierite modified with α-Al2O3 blocking the macroporosity of the cordierite and rounding the channel cross section, on which, a uniform carbon layer was applied by carbonization of a polyfurfuryl alcohol coating obtained by dipcoating. The other two monolithic supports were composite carbon/ceramic monoliths (MeadWestvaco Corporation, USA), a micro- (WA) and a mesoporous (WB) sample. The Pd/HPM catalyst shows a superior selectivity performance compared to the other two samples in the partial hydrogenation of FAME, in terms of the much lower formation of trans double bonds at similar levels of the double bond hydrogenation. This is ascribed to an optimal supply of the reactants and removal of products by only external mass transfer to the nearly nonporous carbon coating. The other two samples suffer from pore diffusion limitations to different extents. [Copyright &y& Elsevier]

Abstract: The hydrogenation of trans,4-phenyl,3-buten,2-one (benzalacetone) and trans,3-phenyl, propenal (cinnamaldehyde) was carried out on Au supported on iron oxides catalysts. Commercial goethite (FeOOH), maghemite (γFe2O3) and hematite (αFe2O3) were used as supports. The catalytic activity of Au/Fe2O3 reference catalyst, supplied by the World Gold Council, was also investigated. Gold catalysts and the parent supports were characterized by BET, X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption of ammonia (NH3-TPD) and high resolution transmission electron microscopy (HRTEM). Among the catalysts investigated Au supported on FeOOH shows the highest activity and selectivity to UA in the hydrogenation of unsaturated carbonyl compounds whereas Au supported on αFe2O3 are the less active and selective catalysts. The catalytic activity and selectivity to unsaturated alcohols (UA) in the hydrogenation of benzalacetone and cinnamaldehyde are less influenced by the morphology of gold particles and are mainly influenced by the nature of the support. A correlation between the reducibility of the catalysts and the activity and selectivity to UA has been found. Increasing the reducibility of the catalysts both the activity and selectivity to UA increase. These results let us to argue that active and selective sites are formed by negative gold particles formed through the electron transfer from the reduced support to the metal. [Copyright &y& Elsevier]

Abstract: Low loading copper catalysts allows hydrogenation of α,β-unsaturated ketones to the corresponding saturated ones with selectivity up to 99%. Moreover, the selectivity can be tuned toward different products only by playing with the support acidity or the experimental conditions. By using a 8% Cu/SiO2 catalyst the final reduction step in the synthesis of the anti-inflammatory drug Nabumetone® can be carried out with selectivity >98% under mild conditions with good productivity and without any additives. No leaching of the metallic phase was observed, the catalyst is not pyrophoric even in the reduced state and it can be reused. [Copyright &y& Elsevier]

Abstract: Three Ru/KL-zeolite catalysts containing 2wt% of Ru were prepared from Ru3(CO)12, RuNO(NO3)3 and Ru(C5H7O2)3 precursors. The samples named Ru(c)/KL, Ru(n)/KL and Ru(a)/KL were studied by temperature-programmed reduction (TPR), by microcalorimetry of CO adsorption, by volumetric hydrogen chemisorption, by X-ray diffraction (XRD) and also by infrared spectroscopy of the CO adsorbed species (CO-FTIR). The catalytic activities and selectivities were evaluated in the hydrogenation of citral at 323K and 5MPa, in a stirred batch reactor. Metal dispersion follows the order Ru(c)/KL>Ru(n)/KL>Ru(a)/KL. The CO-FTIR spectra show a set of different ruthenium species on the support, suggesting the presence of large metal particle outside the zeolite and small crystallites inside the channels, the latter being majority in the Ru(c)/KL sample. Hydrogenation activity per surface metal atom (TOF) was found to be independent on the metal dispersion and, consequently, on the precursor used. The selectivity towards unsaturated alcohols (geraniol+nerol) is in the order Ru(c)/KL

Abstract: Dimethyl adipate hydrogenations catalyzed by Pt/Al2O3 and Pt/TiO2 have been studied. Catalysts were prepared with the conventional impregnation method. Physical–chemical characterization of the catalytic systems was made with the use of different techniques: N2 and H2 sorption, scanning electron microscopy (SEM), energy-dispersive electron (EDS) probe X-ray analysis, temperature programmed reduction (TPR) and inductively coupled plasma optics emission spectrometry (ICP-OES). Metals dispersion in the catalysts is directly related to the superficial area of the supports, and partially covered particles (in the case of the TiO2) can be present. Support modifies the behavior of metals in its surface for different ways: SMSI effect (TiO2) or acidity (Al2O3). The catalyst supported on Al2O3 is more active, reaching 52.91% conversion after 10h of reaction, while at the same period of time, the catalyst supported on TiO2 converted only 15.56% of the substrate. Methyl caproate, adipic acid mono-methyl ester and caprolactone were obtained as main products by Pt/Al2O3 catalyst. These products indicate that carboxylic groups have not been activated enough, leading to formation of significant amount of hydrogenation products different from 1,6-hexanediol (diol). Pt/TiO2 catalyst obtained methyl caproate, caprolactone, hexane and diol, where hexane formation occurred from methyl caproate. Diol formation occurred after 5h of reaction and it indicates participation of platinum and TiO2 as active catalytic sites. [Copyright &y& Elsevier]

The Ni-B and Co-B amorphous alloys exhibited much higher activity and selectivity to ethylamine (C2H5NH2) than their corresponding crystallized counterparts and Raney Ni during liquid phase hydrogenation of acetonitrile (CH3CN). In comparison with the Ni-B amorphous alloy, the Co-B amorphous alloy exhibited longer lifetime and better selectivity, though its activity was slightly lower. The maximum yield of C2H5NH2 could reach 93.5%, showing a good potential in industrial application. The higher activity of the amorphous alloys could be attributed to the large active surface area, the unique amorphous structure together with the suitable structural parameters, and the electron donation of the alloying B to the metallic Ni or Co. The resulted electron-enriched metallic active sites may also account for the better selectivity to C2H5NH2 of the amorphous alloys since, on one hand, it could promote the hydrogenation of CH3CH&z.dbnd6;NH toward C2H5NH2 by activating the C&z.dbnd6;N bond; and on the other hand, it may retard the condensation between CH3CH&z.dbnd6;NH and C2H5NH2 leading to (C2H5)2NH by inhibiting the adsorption of C2H5NH2 which was essential for the condensation. The Co-B amorphous alloy was more selective than the Ni-B owing to its stronger adsorption for CH3CN and the higher electron density on the Co active sites, both of them could inhibit the adsorption for C2H5NH2 and in turn, retard the condensation. This could also account for its longer lifetime. However, such stronger adsorption for CH3CN was harmful for the competitive adsorption for hydrogen and in turn resulted in a slightly lower hydrogenation activity than the Ni-B since the CH3CN hydrogenation was first-order with respect to hydrogen while zero-order to CH3CN. [Copyright &y& Elsevier]

For the selective hydrogenation of acetylene, the novel Pd/α-Al2O3 catalysts prepared by plasma method were investigated. The influence of the preparation method, content of Pd active component, catalyst promoter and reaction temperature has been investigated. It was found that the conversion and selectivity of the catalysts prepared by glow discharge plasma were superior to those obtained from the conventional catalysts. The acetylene conversion of 100% and the selectivity of 71.3% in C2H4 were obtained at 50 °C over the plasma-prepared sample (0.15 wt.% Pd), while the plasma-prepared catalyst was stable during the long-time test for more than 20 h. [Copyright &y& Elsevier]

A steady state model of a trickle-bed reactor is developed for the consecutive hydrogenation of 1,5,9-cyclododecatriene on a Pd/Al2O3 catalyst. Various experiments have shown that the selectivity of this reaction towards the product of interest is much lower in co-current down-flow (trickle-bed) than in up-flow. This is due to uneven liquid distribution and to partial wetting of the catalyst surface at low liquid flow rates.The non-isothermal heterogeneous model proposed here takes into account the partial wetting of the catalyst, as well as the resistances to heat and mass transfer at the gas–liquid, liquid–solid and solid–gas interfaces. It assumes that the catalyst particles can be divided into two distinct concentration zones corresponding to the wetted and dry catalyst surfaces; mass transfer between these two zones is described by a simplified diffusion mechanism.Compared to previous models assuming a uniform concentration of liquid-phase components inside the catalyst particles, this model improves the prediction of the outlet concentrations of hydrogenation products. [Copyright &y& Elsevier]

Silica, titania, zirconia and alumina supported gold particles of 1–6 nm size, prepared by various synthetic routes (sol–gel technique, deposition–precipitation, metal organic-chemical vapor deposition, impregnation, dip-coating) were employed in the selective hydrogenation of acrolein, crotonaldehyde and 1,3-butadiene and in the low-temperature oxidation of carbon monoxide. In-depth characterization of their structural and electronic properties by transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) was aimed at disclosing the nature of the active sites controlling the hydrogenation and oxidation reactions. The structural characteristics such as mean particle size, size distribution and dispersion depend both on the synthetic method employed and the nature of the support. For extremely small gold particles on titania and zirconia (1.1 and 1.4 nm mean size), conduction electron spin resonance of the metal and paramagnetic F-centers (trapped electrons in oxygen vacancies) of the support were observed. The marked structure-sensitivity observed for hydrogenation properties with decreasing particle size may be attributed to structural and electronic properties due to the quantum-size effect of sufficiently small gold particles. Furthermore, the adaptability of gold particles in coatings is demonstrated for a microchannel reactor. [Copyright &y& Elsevier]

It is now apparent that a potential role exists for Au catalysts in the field of chemical processing, in contrast to pollution abatement. This development is prompted by the observation that supported gold catalysts can be a catalyst of choice for some reactions. The recent literature concerning two of these reactions is briefly reviewed in this article, namely: (a) the hydrochlorination of ethyne to produce vinyl chloride; (b) the hydrogenation of α, β unsaturated aldehydes to produce the unsaturated alcohol. For the first of these examples, a correlation between the catalyst activity and the standard electrode potential was used as the basis for predicting that gold would be the best catalyst for this reaction. [Copyright &y& Elsevier]