Active Sites For Hydrogenation Research Articles

Highly efficient Zn-MOF derived Carbon-Nitrogen material based catalyst for nitroaromatic Hydrogenation: The role of Zn-O-C bond and Pyridinic-N

Zn-based catalysts have great feature of environmental friendliness and developmental potential to replace precious metals in heterogeneous catalytic hydrogenation. In this work, a porous CN material-based catalysts containing trace Zn were prepared by high-temperature pyrolysis using zeolitic imidazolate framework (ZIF-8) material as precursor. The result shows that (Zn)NC-800 and (Zn)NC-600–700 exhibit outstanding hydrogenation ability and good stability in nitro compounds hydrogenation reaction. Based on the results of characterization and DFT calculations, two hydrogenation active sites complete the hydrogenation of nitro compounds in (Zn)NC-800 and (Zn)NC-600–700: the residual trace Zn in the form of Zn-O-C bond can activate the CN structure and promote the conversion of nitrobenzene; the pyridinic-N is confirmed to accelerate the electron transfer and enhance the selectivity to aniline. This work has an enlightening significance for the efficient development of heterogeneous catalytic hydrogenation catalysts.

Selective benzene hydroalkylation: Ni/Ni PS/HY catalysts for enhanced cyclohexylbenzene formation

The potential for synthesizing cyclohexylbenzene through one-step hydroalkylation of benzene is significant, but the selectivity is hindered by the deep hydrogenation of benzene to cyclohexane. In this study, Ni-containing phyllosilicate (Ni PS) was incorporated between Ni nanoparticles and zeolite (HY) using the deposition–precipitation technique, thereby creating Ni/Ni PS/HY. A conventional Ni/HY catalyst was also prepared using the impregnation method for comparison. Ni/Ni PS/HY demonstrates outstanding catalytic performance even at a low temperature of 130 °C and a high WHSV of up to 42.21 h−1, achieving a benzene conversion of ∼25 % and a cyclohexylbenzene selectivity of ∼85 %, which remained stable for 300 h. By contrast, the conventional Ni/HY catalyst yields a mere 2.5 % benzene conversion under identical conditions. Comprehensive characterizations and density functional theory (DFT) calculations reveal that Ni PS plays crucial roles in the hydroalkylation of benzene to cyclohexylbenzene. The formation of Ni PS leads to high Ni dispersion, generating more active sites for hydrogenation. Concurrently, the robust interaction between Ni PS and Ni reduces the reactivity of adsorbed H species, impeding the deep hydrogenation of benzene to cyclohexane, while still effectively allowing the formation of cyclohexene. After being adsorbed by the strong acid sites within Ni PS, the intermediate cyclohexene can be smoothly transported through the mesoporous structure of Ni PS to HY for alkylation. All these factors culminate in the exceptional catalytic performance of Ni/Ni-PS/HY.

Efficient conversion of lignin-derived phenols to cycloalkanes over bifunctional catalysts with low loading of ruthenium

Hydrodeoxygenation (HDO) reactions are extensively employed in the conversion of biomass to advanced fuels, which rely heavily on bifunctional catalysts that contain both a metal component and an acidic component. A significant challenge in the development of HDO catalysts is the need to reduce costs while simultaneously enhancing catalytic efficiency. Here, a series of Ru@W/ZrO2 catalysts with an extremely low loading of Ru (0.5 wt%) were successfully synthesized using different Ru or W loading sequences and different Ru/W mass ratios. The catalysts were applied in the HDO reaction of lignin-derived phenols, and their physical and chemical characteristics were revealed by various characterization techniques, including XRD, H2-TPD, NH3-TPD, and XPS. The results suggest that the synthesis method with post-loading Ru leads to improved exposure and utilization of the low-loaded Ru, which effectively serves as the active sites for hydrogenation in catalytic reactions. Under the same reaction conditions, the bifunctional catalyst with post-loading of Ru achieved a complete conversion of phenol into cyclohexane, while the catalyst with simultaneous loading of Ru and W only yielded 42% of cyclohexane. In addition, the Ru/W ratios have also shown significant effects on the HDO performance of the catalyst. The catalyst exhibits the highest hydrogenation activity when the Ru/W ratio is 10, which is further supported by kinetic experiments. This study highlights the significance of the loading sequence of noble metals and the metal/acid ratio in the synthesis of highly active bifunctional catalysts, and also lays the groundwork for the efficient utilization of noble metals in biomass HDO conversion.

Protein–metal ion networks coated carbon matrix as a precursor: to construct carbon-supported Mo-based catalysts with highly exposed active sites for hydrogenation of nitro compounds

Protein–metal ion networks coated carbon matrices were employed as a precursor for preparing carbon-supported Mo-based catalysts with highly exposed active sites for nitro hydrogenation.

Cu/Nb2O5 composite aerogel for CO2 hydrogenation to methanol: Construction of porous structure and abundant active interfaces

Catalytic conversion of CO2 offers a promising method to mitigate the green-house gas and recycle CO2 into value-added chemicals. Cu-based aerogels hold the potential as high-performance catalysts due to the three-dimensional morphology, high porosity, and self-supporting skeletons. Herein, we successfully applied Cu/Nb2O5 composite aerogel into CO2 hydrogenation, which achieved high production rate and selectivity towards methanol. Further mechanism study demonstrated that abundant interfaces between Cu and Nb2O5 were formed throughout the porous networks of Cu/Nb2O5 aerogel, acting as the active sites for the adsorption, activation, and selective conversion of CO2. Besides, the production of methanol was via the formate pathway over Cu/Nb2O5. This work opens up an appealing approach for the design of efficient catalysts with rich active sites for hydrogenation of CO2.

In situ construction of 3D NiMo bimetallic catalysts anchored on dendritic mesoporous silica for the upgrading of biomass derivatives

Reasonable construction of bi-function catalysts with well dispersed hydrogenation active sites and acidic sites are crucial for the hydrodeoxygenation (HDO) of biomass-derived compounds but still a huge challenge. Herein, a 3D Mo functionalized Ni-based bimetallic embedded catalyst with fine metal nanoparticles size (<6 nm) was prepared for the first time using dendritic mesoporous silica as a sacrificial template by one-pot hydrothermal synthesis and adopted in the HDO process of vanillin (VAN) upgrade to 2-methoxy-4-methylphenol (MMP). The characterization results illustrated that Mo species regulated the acidity of the catalyst and promoted the formation of Ni-Mo alloy sites. Density functional theory (DFT) calculations further unveiled that Ni-Mo alloy sites promoted the activation and dissociation of CO bond in VAN, enhanced the ability of protonation hydrogenolysis. Benefitting from the synergistic effect of the highly uniformly dispersed hydrogenation metal sites and acidic sites, nearly 100% yield of MMP could obtained over the designed catalyst under mild conditions (130 °C, 1.5 MPa H2, 3 h, 10 wt% catalyst dosage). Additionally, the NiMo0.1@MSN catalyst displayed robust activity for no less than 8 recycles and excellent universality for the HDO of a variety of lignin derivatives and biomass platform molecules, which provide a feasible strategy for the construction of 3D confined catalysts for the high-efficiency HDO of biomass derivatives.

Highly Efficient Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol over CoRe/TiO2 Catalyst.

Allylic alcohols typically produced through selective hydrogenation of α,β-unsaturated aldehydes are important intermediates in fine chemical industry, but it is still a challenge to achieve its high selectivity transformation. Herein, we report a series of TiO2-supported CoRe bimetallic catalysts for the selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) using formic acid (FA) as a hydrogen donor. The resultant catalyst with the optimized Co/Re ratio of 1:1 can achieve an exceptional COL selectivity of 89% with a CAL conversion of 99% under mild conditions of 140 °C for 4 h, and the catalyst can be reused four times without loss of activity. Meanwhile, the Co1Re1/TiO2/FA system was efficient for the selective hydrogenation of various α,β-unsaturated aldehydes to the corresponding α,β-unsaturated alcohols. The presence of ReOx on the Co1Re1/TiO2 catalyst surface was advantageous to the adsorption of C=O, and the ultrafine Co nanoparticles provided abundant hydrogenation active sites for the selective hydrogenation. Moreover, FA as a hydrogen donor improved the selectivity to α,β-unsaturated alcohols.

Rational design for the fabrication of bulk Ni3Sn2 alloy catalysts for the synthesis of 1,4-pentanediol from biomass-derived furfural without acidic co-catalysts.

This study describes the rational design for the fabrication of bulk Ni3Sn2 alloy catalysts for the de/hydration-hydrogenation of biomass-derived furfural (FFald) to 1,4-pentanediol (1,4-PeD) without the acidic co-catalyst. The presence of both hydration active sites (Brønsted acid sites (Ni-SnOx)) and hydrogenation active sites (Ni0 or Ni-Sn alloy) in Ni3Sn2 alloy could be controlled by changing the pH of Ni-Sn solution during the preparation. Both active sites acted synergistically to catalyse the de/hydration-hydrogenation reactions of FFald to produce a high yield of 1,4-PeD in a batch reaction system at 433 K, 3.0 MPa H2 after 12 h. Bulk Ni3Sn2 obtained at pH of Ni-Sn solution of 8-10, hydrothermal temperature of 423 K for 24 h, and reduction with H2 at 673 K for 1.5 h demonstrated a high yield of 1,4-PeD (81-87%), which is comparable with that from previous work. A 76% yield of 1,4-PeD was also obtained when the reaction was carried out in a fixed-bed reaction system at 433 K, flow rate 0.065 mL min-1, H2 flow rate 70 mL min-1, and 3.29 wt% FFald in H2O/ethanol solution for 12 h. The activity of bulk Ni3Sn2 was maintained with 66% yield of 1,4-PeD even after 52 h reaction on stream. The fabricated bulk Ni3Sn2 alloy catalysts could be the promising heterogeneous Ni-Sn alloy-based catalysts for the catalytic conversion of biomass-derived-furanic compounds (e.g., FFald, furfuryl alcohol (FFalc), and 2-methylfuran (2-MeF)).

Constructing layer-by-layer self-assembly MoS2/C nanomaterials by a one-step hydrothermal method for catalytic hydrogenation of phenanthrene.

Layer-by-layer self-assembly MoS2/C nanomaterials are constructed through the electrostatic adsorption between MoS2 nuclei with positive charge and C nuclei with negative charge using a facile one-step hydrothermal method. The layer-by-layer self-assembly MoS2/C catalysts with high exposure of catalytic hydrogenation active sites exhibit enhanced catalytic performance in phenanthrene hydrogenation.

Highly dispersed platinum clusters anchored on hollow ZSM-5 zeolite for deep hydrogenation of polycyclic aromatic hydrocarbons

• The hollow hierarchical ZSM-5 supported Pt catalyst was synthesized by SEA method. • SEA can boost metal dispersion and formation of electron-deficient Pt δ+ species. • The Pt δ+ species combing acidic sites presented excellent deep hydrogenation ability. • DFT calculations confirmed that the Pt δ+ species can enhance the adsorption of PAHs. • Pt/HZ-SEA showed excellent PHE intrinsic hydrogenation activity and sulfur-resistant. Deep hydrogenation of polycyclic aromatic hydrocarbons is a feasible strategy to acquire high-performance aviation fuels, in which the key is to design highly active hydrogenation catalysts. Herein, hollow ZSM-5 (HZ) and silicalite-1 (HS) zeolites with hierarchical porous architectures were manufactured through a post-alkali treatment strategy, and further supported Pt to fabricate Pt/HZ-WI, Pt/HZ-SEA and Pt/HS-SEA catalysts employing wet impregnation (WI) and strong electrostatic adsorption (SEA) methods. The SEA catalysts presented higher metal dispersion, more election-deficient Pt δ+ species and stronger spillover hydrogen ability, thus resulting in better intrinsic hydrogenation properties in the deep hydrogenation reaction of phenanthrene than the WI ones. Moreover, Pt/HZ-SEA catalyst showed the supreme catalytic activity and the lowest activation energy of 52.11 kJ·mol −1 due to more hydrogenation active sites generated by the highly dispersed Pt clusters and the accelerated diffusion of reactants via the hierarchical porous architectures. Almost 100% selectivity to the deep hydrogenation products was achieved at rather low temperature of 220 °C. The Pt/HZ-SEA also displayed outstanding activity for hydrogenation of naphthalene, acenaphthylene and fluorene and excellent sulfur resistance. Furthermore, the acidic sites in HZ zeolite were favorable to boost the formation of electron-deficient Pt δ+ species having stronger deep hydrogenation ability and intensify the additional hydrogenation route through the spillover hydrogen. Finally, the DFT calculation results further verified that the Pt δ+ substances could heighten the adsorption of polyaromatics, thereby improving the deep hydrogenation activity.

Cobalt-Graphene Catalyst for Selective Hydrodeoxygenation of Guaiacol to Cyclohexanol.

Herein, cobalt-reduced graphene oxide (rGO) catalyst was synthesized with a practical impregnation–calcination approach for the selective hydrodeoxygenation (HDO) of guaiacol to cyclohexanol. The synthesized Co/rGO was characterized by transmission electron microscopy (TEM), high-angle annular dark-field scanning TEM (HAADF-STEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD), and H2 temperature-programmed reduction (H2-TPR) analysis. According to the comprehensive characterization results, the catalyst contains single Co atoms in the graphene matrix and Co oxide nanoparticles (CoOx) on the graphene surface. The isolated Co atoms embedded in the rGO matrix form stable metal carbides (CoCx), which constitute catalytically active sites for hydrogenation. The rGO material with proper amounts of N heteroatoms and lattice defects becomes a suitable graphene material for fabricating the catalyst. The Co/rGO catalyst without prereduction treatment leads to the complete conversion of guaiacol with 93.2% selectivity to cyclohexanol under mild conditions. The remarkable HDO capability of the Co/rGO catalyst is attributed to the unique metal–acid synergy between the CoCx sites and the acid sites of the CoOx nanoparticles. The CoCx sites provide H while the acid sites of CoOx nanoparticles bind the C-O group of reactants to the surface, allowing easier C-O scission. The reaction pathways were characterized based on the observed reaction–product distributions. The effects of the process parameters on catalyst preparation and the HDO reaction, as well as the reusability of the catalyst, were systematically investigated.

Synthesis of Dual-Active-Sites Ni-Ni2In catalysts for selective hydrogenation of furfural to furfuryl alcohol

The rational design of efficient heterogeneous catalysts for selective hydrogenation of unsaturated aldehyde to unsaturated alcohol is a long-term scientific challenge and pursuit. Herein, we prepared an effective NiIn0.2/MgO-Al2O3 catalyst with dual active sites for hydrogenation of furfural (FAL) to furfuryl alcohol (FOL), delivering a high activity and a maximum 98.9% FOL yield. Moreover, the NiIn0.2/MgO-Al2O3 exhibited excellent catalytic performances for the other unsaturated aldehydes and good durability in a 100 h stability test. Characterization and theoretical calculations reveal that H2 and FAL are adsorbed and activated on the active sites of metallic Ni and Ni2In intermetallic compound, respectively. Hydrogenation of FAL to FOL occurs on the surface of Ni2In via hydrogen spillover from metallic Ni. Sequentially, FOL easily desorbs from the surface of Ni2In owing to the active-site isolation and electron transfer effect in Ni2In. The metal-IMCs dual-active-sites mechanism provides a novel strategy for synthesizing efficient hydrogenation catalysts.

Preparation of Porous NiCe Composite Catalyst and Its Performance for CO2 Hydrogenation

AbstractNi component can be effectively introduced into CeO2 by a soft template method to prepare porous NiCe composite catalysts. The reducibility of the catalyst precursors was studied by H2‐TPR. The physicochemical properties of the prepared NiCe composite catalysts were characterized by XRD, quasi in‐situ XPS, BET and TEM. And the catalytic performances of the corresponding NiCe composite catalysts was evaluated by CO2 catalytic hydrogenation. The synergistic effect of Ni and Ce species can significantly improve the reducibility of the precursors to form CO2 hydrogenation active sites in the corresponding NiCe composite catalysts. The morphology, pore structure, specific surface area, crystallinity and content of metal Ni species of the prepared NiCe composite catalysts were significantly affected by nNi/nCe ratio, which can affect the CO2 catalytic hydrogenation performances of NiCe composite catalysts. The synergistic effect of Ni and Ce species can also promote the formation of NiCe composite catalyst nanoparticles with small particle size about 5–10 nm. The developed mesoporous structure and high specific surface area can be formed in the prepared NiCe composite catalysts. The NC3 catalyst with a nNi/nCe ratio of 3.0 showed the best CO2 hydroreduction performances and use stability. When the reaction temperature was 300 °C, the CO2 conversion and CH4 selectivity can reach 85.6% and 100%, respectively. Even if the reaction temperature rises to 340 °C, the CO2 conversion and CH4 selectivity can be maintained at 83.7% and 100% in the continuous reaction of 600 min, respectively.

Di- and Tetrameric Molybdenum Sulfide Clusters Activate and Stabilize Dihydrogen as Hydrides

NaY zeolite-encapsulated dimeric (Mo2S4) and tetrameric (Mo4S4) molybdenum sulfide clusters stabilize hydrogen as hydride binding to Mo atoms. Density functional theory (DFT) calculations and adsorption measurements suggest that stabilization of hydrogen as sulfhydryl (SH) groups, as typical for layered MoS2, is thermodynamically disfavored. Competitive adsorption of H2 and ethene on Mo was probed by quantifying adsorbed CO on partly hydrogen and/or ethene covered samples with IR spectroscopy. During hydrogenation, experiment and theory suggest that Mo is covered predominately with ethene and sparsely with hydride. DFT calculations further predict that, under reaction conditions, each MoxSy cluster can activate only one H2, suggesting that the entire cluster (irrespective of its nuclearity) acts as one active site for hydrogenation. The nearly identical turnover frequencies (24.7 ± 3.3 molethane·h–1·molcluster–1), apparent activation energies (31–32 kJ·mol–1), and reaction orders (∼0.5 in ethene and ∼1.0 in H2) show that the active sites in both clusters are catalytically indistinguishable.

Intermetallic YIr2 nanoparticles with negatively charged Ir active sites for catalytic hydrogenation of cyclohexanone to cyclohexanol

Negatively charged iridium species in Laves phase YIr2 as highly active sites for hydrogenation of cyclohexanone to cyclohexanol.

A Review on the Hydroisomerisasion of n-Parafins over Supported Metal Catalysts

Catalytic hydroisomerization of n-paraffin aims to produce branched paraffin isomers and suppress cracking reactions in the production of the low cloud point of biodiesel. The development of the type of metal and catalyst support, amount of metal loading, and reaction conditions are important to increase the catalyst activity. A high performace catalyst for hydroisomerization bears bifunctional characteristics with a high level of hydrogenation active sites and low acidity, maximizing the progress of hydroisomerization compared to the competitive cracking reaction. In addition, a catalyst support with smaller pore size can hinder large molecular structure isoparaffins to react on the acid site in the pore thus providing good selectivity for converting n-paraffin. Catalysts loaded with noble metals (Pt or Pd) showed significantly higher selectivity for hydroisomerization than non-noble transition metals such as Ni, Co, Mo and W. The reaction temperature and contact time are also important parameters in hydroisomerization of long chain paraffin, because long contact times and high temperatures tend to produce undesired byproducts of cracking. This review reports several examples of supported metal catalyst used in the hydroisomerization of long chain hydrocarbon n-paraffins under optimized reaction conditions, providing the best isomerization selectivity results with the lowest amount of byproducts. The role of various metals and their supports will be explained mainly for bifunctional catalysts.

Water-mediated hydrogen spillover accelerates hydrogenative ring-rearrangement of furfurals to cyclic compounds

Upgrading bioderived furfurals (furfural, 5-hydroxymethylfurfural) to cyclopentanones (cyclopentanone, 3-hydroxymethylcyclopentanone) and cyclopentanols (cyclopentanol, 3-hydroxymethylcyclopentanol) is a representative bifunctional catalytic process in biomass conversion. Here, a class of Pd/NiMoO4 catalysts (Pd/NiMoO4-Cl, Pd/NiMoO4-AC) with low Pd loading (1.0 wt%) and different Pd dispersion are synthesized. The hydrogenation active sites and acidic sites of catalysts were adjusted by a water-mediated hydrogen spillover process. 56.3–85.3% yields of cyclopentanones and 65.4–85.2% yields of cyclopentanols were obtained by hydrogenative ring-rearrangement route of furfurals over Pd/NiMoO4-Cl and Pd/NiMoO4-AC, respectively. Over-hydrogenated byproducts (tetrahydrofurfuryl alcohol, 2,5-bis(hydroxymethyl)tetrahydrofuran) with a yield above 54% were generated by a full hydrogenation route over Pd/C. The difference in catalytic performance is results from alteration of the adsorption configurations of reactants and the transformation of Lewis acid sites to Brønsted acid sites by hydrogen spillover. This work presents an effective strategy for governing reaction routes and enhancing bifunctional catalysis with a hydrogen spillover mechanism.

Synthesis and consequence of Zn modified ZSM-5 zeolite supported Ni catalyst for catalytic aromatization of olefin/paraffin

Zn modified ZSM-5 zeolite supported Ni bifunctional catalysts were prepared by in-situ hydrothermal synthesis (Zn-Ni-ZSM-5), co-impregnation method (Zn-Ni/ZSM-5) as well as combining in-situ hydrothermal synthesis of Zn-ZSM-5 and sequential impregnation of Ni (Ni/Zn-ZSM-5) and used for the selective converting olefin to aromatics applicable for FCC gasoline hydro-upgrading. The Lewis (L) acid sites generated by ZnOH+ species and hydrogenation active sites from Ni0 species were varied with preparation method, in which their locations at the external surface or micropores of zeolite changed the acid properties of catalysts. Comparing to the Zn-Ni/ZSM-5 from the co-impregnation method, direct in-situ hydrothermal method could incorporate Zn and Ni species within zeolite, which makes the strong interaction between the metal species and the framework Al to form medium-strong L acids (ZnOH+/NiOH+). This leads to the decrease of ratio of Brønsted acid sites to L acid sites (B/L) from 0.40 to 0.12 and the difficulty in reducing of Ni cations to Ni0 from 57% to 30% Ni0 percent. Ni/Zn-ZSM-5 sample prepared by incorporating Zn species into micropores and sequential depositing Ni species at the external surface of zeolite possesses a low B/L ratio similar to Zn-Ni-ZSM-5 (0.20 versus 0.12) but a much higher Ni0 percent (52% versus 30%). Zn-Ni-ZSM-5 shows closer intimacy between Zn and Ni species comparing to Zn-Ni/ZSM-5 and Ni/Zn-ZSM-5. For the 1-hexene aromatization, the formed iso-alkene at acid sites was quickly saturated to iso-alkanes by the adjacent Ni0 particles over Ni-Zn-ZSM-5 catalyst in hydrogen steam. However, the location of aromatization active sites (ZnOH+, L acid sites) in micropores and hydrogenation active sites (Ni0 species) on external surface of Ni/Zn-ZSM-5 makes the tandem conversion of n-alkene → iso-alkene → aromatics, rather than the n-alkene → iso-alkene → iso-alkane. Thus, Zn-Ni-ZSM-5 with close intimacy of ZnOH+ and Ni0 particles shows a high iso-alkane selectivity (27.9% iC4+), while Ni/Zn-ZSM-5 exhibits a high aromatics selectivity (39.6 %) in the conversion of 1-hexene in hydrogen steam. Similar results have also found in the conversion of n-heptane. Here, the control of the intimacy of Zn and Ni in ZSM-5 zeolites has been realized to be a good protocol to adjust the selective conversion of olefins/alkanes to aromatics versus iso-alkanes.

Engineering hydrogenation active sites on graphene oxide and N-doped graphene by plasma treatment

Graphene oxide (GO) and N-doped graphene [(N)G] graphenes were submitted to H2 glow discharge under different discharge regimes, in both the negative glow and positive column plasma regions. The resulted catalysts were fully characterized using several techniques such as Raman, DRIFT and XPS spectroscopy, powder X-ray diffraction, H2 pulse chemisorption and H2-, CO2- and NH3-TPD experiments. Density functional theory calculations were performed taking a slab model of graphene sheet with an optimized CC bond length (1.426 Å) and a 16 Å vacuum layer between sheets. An overview of these characterizations showed that the O/C atomic ratio of GO is influenced by the plasma regime, indicating the occurrence of O removal, as also predicted by DFT calculations. In the case of (N)G, the plasma treatment also removes pyridinic N with an increase of the C/N ratio. The efficiency of the plasma modification has been checked through catalytic tests in hydroisomerization of 1-octene and hydrogenation of α-methyl-styrene. Contrarily to classical thermal activation requiring high temperatures, the generation of the defects by treating with plasma occurs at voltages in the range of 2−5 kV. In consequence, the hydrogenation and isomerization of alkenes resulted with high yields and good selectivities. Graphene prepared from sodium alginate from brown algae was considered as reference in these investigations.

Manganese containing copper aluminate catalysts: Genesis of structures and active sites for hydrogenation of aldehydes

Copper aluminate spinel (CuO.CuAl2O4) is the favoured Cr-free substitute for the copper chromite catalyst (CuO.CuCr2O4) in the industrial hydrogenation of aldehydes. New insights in the catalytic mechanism were obtained by systematically studying the structure and activity of these catalysts including effects of manganese as a catalyst component. The hydrogenation of butyraldehyde to butanol was studied as a model reaction and the active structure was characterised using X-ray diffraction, temperature programmed reduction, N2O chemisorption, EXAFS and XANES, including in-situ investigations. The active catalyst is a reduced spinel lattice that is stabilised by protons, with copper metal nanoparticles grown upon its surface. Incorporation of Mn into the spinel lattice has a profound effect on the spinel structure. Mn stabilises the spinel towards reduction of CuII to Cu0 by occupation of tetrahedral sites with Mn cations, but also causes decreased catalytic activity. Structural data, combined with the effect on catalysis, indicate a predominantly interface-based reaction mechanism, involving both the spinel and copper nanoparticle surface in protonation and reduction of the aldehyde. The electron reservoir of the metallic copper particles is regenerated by the dissociative adsorption and oxidation of H2 on the metal surface. The generated protons are stored in the spinel phase, acting as proton reservoir. Cu(I) species located within the spinel and identified by XANES are probably not involved in the catalytic cycle.