Heterogeneous Catalytic Hydrogenation Research Articles

Application of parahydrogen for mechanistic investigations of heterogeneous catalytic processes

Parahydrogen-induced polarization technique (PHIP), based on the pairwise addition of molecular hydrogen to a substrate, was successfully applied to obtain novel information on the mechanisms of heterogeneous catalytic hydrogenation, hydrodesulfurization, and oligomerization processes. In particular, the PHIP effects were observed upon hydrogenation with parahydrogen catalyzed by the immobilized neutral complexes of rhodium and iridium, which confirms the similarity in the mechanisms of homogeneous and heterogeneous hydrogenation for such systems. In the study of acetylene oligomerization, a significant NMR signal enhancement was revealed for a number of C4 oligomers, with the enhancement levels by far exceeding that observed in hydrogenation of carbon-carbon triple bonds. The mechanistic features of heterogeneous hydrogenation of a number of six-membered cyclic hydrocarbons over supported metal catalysts were investigated, and their hydrogenation scheme based on the pairwise addition of molecular hydrogen was proposed. Furthermore, the PHIP technique revealed that heterogeneous hydrodesulfurization of thiophene mainly proceeds via hydrogenation followed by a C—S bond cleavage. A significant enhancement of sensitivity in combination with characteristic line shapes of NMR signals make the PHIP method a unique and highly informative tool for the investigation of heterogeneous catalytic processes.

Theoretical understanding on the selectivity of acrolein hydrogenation over silver surfaces: the non-Horiuti–Polanyi mechanism is the key

The significance of the non-Horiuti–Polanyi mechanism in understanding heterogeneous catalytic hydrogenation reactions is highlighted.

Heterogeneous catalytic hydrogenation of CO2 by metal oxides: defect engineering - perfecting imperfection.

Metal oxides with their myriad compositions, structures and bonding exhibit an incredibly diverse range of properties. It is however the defects in metal oxides that endow them with a variety of functions and it is the ability to chemically tailor the type, population and distribution of defects on the surface and in the bulk of metal oxides that delivers utility in different applications. In this Tutorial Review, we discuss how metal oxides with designed defects can be synthesized and engineered, to enable heterogeneous catalytic hydrogenation of gaseous carbon dioxide to chemicals and fuels. If this approach to utilization and valorization of carbon dioxide could be developed at industrially significant rates, efficiencies and scales and made economically competitive with fossil-based chemicals and fuels, then carbon dioxide refineries envisioned in the future would be able to contribute to the reduction of greenhouse gas emissions, ameliorate climate changes, provide energy security and enable protection of the environment. This would bring the vision of a sustainable future closer to reality.

Synthesis of Aminoindolizidines through the Chemoselective and Diastereoselective Catalytic Hydrogenation of Indolizines.

Indolizidines are bioactive heterocyclic compounds of great potential normally prepared following multistep routes. However, to the best of our knowledge, the synthesis of 1-aminoindolizidines has never been reported. Herein, 1-(dialkylamino)-3-substituted indolizidines have been straightforwardly synthesized using an atom-economic protocol that involves a copper-catalyzed three-component synthesis of indolizines followed by heterogeneous catalytic hydrogenation. The latter was found to be chemoselective using platinum(IV) oxide as the catalyst at 3.7 atm, providing the aminoindolizidines in modest-to-high yields (35-95%) and high diastereoselectivity (92:8 to >99:1). It has been experimentally demonstrated that the hydrogenation occurs through the intermediate 5,6,7,8-tetrahydroindolizine, which contains a pyrrole moiety. Moreover, the diastereomerically pure 1-(dibenzylamino)-3-substituted indolizidines could be further transformed into the corresponding monobenzylated or fully debenzylated aminoindolizidines by selective hydrogenolysis catalyzed by Pt/C or Pd/C, respectively, under ambient conditions.

Iron Oxide as a Catalyst for Nitroarene Hydrogenation: Important Role of Oxygen Vacancies

Heterogeneous catalytic hydrogenation of nitroarenes is one of the most important chemical transformations, and exploring earth-abundant catalysts is very attractive for application. Herein, we studied the catalytic activity of several iron oxide catalysts with similar structure and surface area. It is found that γ-Fe2O3, α-Fe2O3, and FeO show obvious but a little limited activity, but the activity of the used catalyst is increased in the second run, especially for γ-Fe2O3. Characterization shows that Fe2O3 is partly reduced with many oxygen vacancies produced on the surface, which accounts for the high hydrogenation activity. Finally, Fe3O4 exhibits activity significantly higher than Fe2O3 and FeO, and 100% selectivity in the hydrogenation of nitroarenes to anilines. Also, Fe3O4 is easy to separate by a magnetic field and shows excellent recycling stability.

Hydrogenation of Unsaturated Six-Membered Cyclic Hydrocarbons Studied by the Parahydrogen-Induced Polarization Technique

Parahydrogen-induced polarization (PHIP) is an efficient technique for mechanistic investigations of homogeneous and heterogeneous catalytic hydrogenations. Herein, heterogeneous gas phase hydrogenation of six-membered cyclic hydrocarbons (benzene, toluene, cyclohexene, 1,3-cyclohexadiene and 1,4-cyclohexadiene) over Rh/TiO2, Pd/TiO2, and Pt/TiO2 catalysts was studied using PHIP. As expected, cyclohexene hydrogenation led to the formation of cyclohexane which because of its symmetry should not exhibit any PHIP effects. However, the presence of 13C nuclei at natural abundance (1.1%) breaks molecular symmetry, resulting in the observation of 13C satellite signals exhibiting PHIP effects in the 1H NMR spectra. In experiments with cyclohexene, the reactant’s NMR signals were also polarized, demonstrating the possibility of cyclohexene dehydrogenation to 1,3-cyclohexadiene and subsequent hydrogenation to cyclohexene. In the hydrogenation of 1,3-cyclohexadiene and 1,4-cyclohexadiene, all NMR signals of cyclohex...

Ni-based structured catalyst for selective 3-phase hydrogenation of nitroaromatics

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=353K; P=10bar). It was shown that metallic Ni0 nanoparticles (NPs) with a mean diameter of ∼2.0nm 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 H2 at T>353K. 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 H2 as the hydrogen source.

Modeling the integrated heterogeneous catalytic fixed-bed reactor and rotating biological contactor system for the treatment of poorly biodegradable industrial agrochemical wastewater

An integrated system based on a heterogeneous catalytic wet hydrogen peroxide oxidation (CWHPO) and subsequent rotating biological contactors (RBCs) has been modeled for the treatment of agrochemical wastewater. One dimensional pseudo-homogeneous model was proposed for the CWHPO step. The reaction rate for TOC removal (k1) was 0.087 1/min. In the case of the RBCs, two different approaches were considered: the pseudo-homogeneous model was based on Kornegy and Clark equations and it is restricted to only one substrate limitation, TOC, for the microbial growth. The microbial growth was modeled by a Monod type equation. The uptake rate and saturation coefficient values were P=0.94g/dm2d and Ks=0.53g/dm3. The integrated non-pseudo-homogeneous model considers a two-phase bioreactor in which all the biochemical processes occur in the solid biofilm phase. In this model, processes such as biofilm growth and diffusion of nutrients into biofilm were taken into account. The microbial growth was modeled using a double Monod equation with substrate limitation by TOC and total nitrogen (TN). Both approaches were able to describe the CWHPO-RBCs performance at different operating conditions with an estimated growth rate (μMAX) of 3.62 1/d. The calculated TOC removal was in good agreement with the experimental results. The two-phase model was also able to predict the TN removal of the system. The modeling of the coupling CWHPO/RBCs process could be a useful guide in order to achieve a cost-effective process leading to optimum C/N composition of the treated effluent and resulting in better overall removal efficiency.

Poly(cyclohexylethylene)-block-Poly(lactide) Oligomers for Ultrasmall Nanopatterning Using Atomic Layer Deposition.

Poly(cyclohexylethylene)-block-poly(lactide) (PCHE-PLA) block polymers were synthesized through a combination of anionic polymerization, heterogeneous catalytic hydrogenation and controlled ring-opening polymerization. Ordered thin films of PCHE-PLA with ultrasmall hexagonally packed cylinders oriented perpendicularly to the substrate surface were prepared by spin-coating and subsequent solvent vapor annealing for use in two distinct templating strategies. In one approach, selective hydrolytic degradation of the PLA domains generated nanoporous PCHE templates with an average pore diameter of 5 ± 1 nm corroborated by atomic force microscopy and grazing incidence small-angle X-ray scattering. Alternatively, sequential infiltration synthesis (SIS) was employed to deposit Al2O3 selectively into the PLA domains of PCHE-PLA thin films. A combination of argon ion milling and O2 reactive ion etching (RIE) enabled the replication of the Al2O3 nanoarray from the PCHE-PLA template on diverse substrates including silicon and gold with feature diameters less than 10 nm.

Recently Used Nanocatalysts in Reduction of Nitroarenes

Nanocatalysis is swiftly mounting in various catalyzed organic reactions. Nowadays a wide variety of nano sized species such as nanoparticles or nanocomposites are effectively employed as catalyst. Conventionally noble metals such as Pt, Pd, Rh and Au are used in various heterogeneous catalytic reductions in organic chemistry. Heterogeneous hydrogenation catalysis is highly desirable since in this stage the important enantio-differentiating step is happening at the metal surface. In this review, we try to underscore the recent development of using the traditional noble metals in their nano forms as nanocatalysts in the reduction of nitroarenes such as 4-nitrophenol (4- NP) and related compounds to their corresponding amino derivatives. Keywords: Nanocatalysts, reduction reaction, nitroarenes, metal nanoparticles.

Heterogeneous Catalytic Transfer Hydrogenation as an Effective Pathway in Biomass Upgrading

Reducing oxygen content in biomass-derived feedstocks via hydrodeoxygenation (HDO) is a key step in their upgrading to fuels and valuable chemicals. Organic molecules, e.g., alcohols and formic acid, can donate hydrogen to reduce the substrate in a process called catalytic transfer hydrogenation (CTH). Although it is practiced far less frequently than molecular-hydrogen-based HDO processes, CTH has been proven to be an efficient and selective strategy in biomass upgrading in the last two decades. In this paper, we present a selective review of recent progress made in the upgrade of biomass-derived feedstocks through heterogeneous CTH, with a focus on the mechanistic interpretation. Hydrogenation and cleavage of C═O and C–O bonds, respectively, are the two main categories of reactions discussed, owing to their importance in the HDO of biomass-derived feedstocks. On acid–base catalysts, Lewis acid–base pair sites, rather than a single acid or base site, mediate hydrogenation of carbonyl groups with alcohols...

Adsorption and Reaction Kinetic Studies of the Heterogeneous Catalytic Hydrogenation for Polystyrene

We applied silica hollow microspheres with through holes in the shell as supports to prepare Pd-based supported catalyst (Pd/SHMs) for heterogeneous catalytic hydrogenation of polystyrene (PS) and also systematically studied the adsorp- tion and reaction behavior of PS molecules over Pd/SHMs. The dynamic adsorption and reaction models of PS molecules under different temperatures have been established and the partially hydrogenated products were also comprehensively ana- lyzed. The result shows that both the adsorption capacity and saturation time are increased as the temperature increasing and this hydrogenation reaction is confirmed to be a first-order reaction and the activation energy is calculated to be 58.3 kJmol -1 . After separating and purifying three samples with different hydrogenation degrees, we further analyzed the partially hydrogenated products and the results show that they are all actually comprised of two kinds of substances with different properties, one with high hydrogenation conversion rate (ca. 85%) and the other with low hydrogenation ratio (ca. 25%). It is proved that PS heterogeneous hydrogenation process exists secondary adsorption and competitive adsorption phenomenon, and obeys the Blocky mechanism. This work lays the foundation for PS adsorption and hydrogenation reaction and is also favorable for the understanding of the adsorption and catalytic process for other unsaturated polymers over heterogeneous catalysts.

Production of Diesel Fuel via Hydrogenation of Rancid Lard and Gas Oil Mixtures

For the second generation bio-fuels the most promising product mixtures are the bio gas oils and diesel fuels containing bio gas oils. These products are in the gas oil boiling point range and made by catalytic hydrogenation of pure triglycerides or triglyceride-gas oil mixtures. The bio gas oil product is a mixture of n- and i-paraffins. During the experimental work our aim was to investigate the heterogeneous catalytic hydrogenation of rancid lard and its 50% mixtures of gas oil fraction on sulphided CoMo/Al2O3 catalyst. During a series of experiments we studied the effects of the different feedstocks (lard content of 50-100%) and the process parameters (temperature: 300-380 °C, pressure 40-80 bar, LHSV: 1.0-2.0 h -1 , H2/feedstock rate: 600 Nm 3 /m 3 ) on the yield and quality of the products. We assessed that in the course of the heterogeneous catalytic hydrogenation the deoxygenation of the triglyceride part of the feedstock occurred while the removal of the sulphur and nitrogen content and the saturation of the aromatic content took place with a high degree as well. In the course of the experiments we managed to make excellent quality products, which are suitable for the use in Diesel-engines.

Poly(cyclohexylethylene)-block-poly(ethylene oxide) Block Polymers for Metal Oxide Templating.

A series of poly(cyclohexylethylene)-block-poly(ethylene oxide) (CEO) diblock copolymers were synthesized through tandem anionic polymerizations and heterogeneous catalytic hydrogenation. Solvent-annealed CEO diblock films were used to template dense arrays of inorganic oxide nanodots via simple spin coating of an inorganic precursor solution atop the ordered film. The substantial chemical dissimilarity of the two blocks enables (i) selective inclusion of the inorganic precursor within the PEO domain and (ii) the formation of exceptionally small feature sizes due to a relatively large interaction parameter estimated from mean-field analysis of the order-disorder transition temperatures of compositionally symmetric samples. UV/ozone treatment following incorporation produces an ordered arrangement of oxide nanodots and simultaneously removes the block polymer template. Herein, we report the smallest particles (6 ± 1 nm) templated from a selective precursor insertion method to date using a block polymer scaffold.

Diesel Fuel Production by Catalytic Hydrogenation of Light Cycle Oil and Waste Cooking Oil Containing Gas Oil

Heterogeneous catalytic hydrogenation of mixtures containing straight run gas oil (70–85 %), light cycle oil (LCO) (15 %) and waste cooking oil (WCO) (0–15 %) was investigated on commercial CoMo/Al2O3 catalyst. We determined that with the application of LCO in the feedstocks the density of the products can be increased. With the formed n- and isoparaffins (from the WCO content of the feedstocks) the higher aromatic content (lower cetane index) of the products—caused by the unconverted LCO components—could be partly compensated and the second generation biocomponent content can be assured. On the pre-sulphided catalyst the best products could be produced in case of T = 360 °C, P = 30 bar, LHSV = 1.0 h−1, H2/feedstock ratio = 420 Nm3/m3 process parameters and 10–15 % WCO content of feedstocks. The polyaromatic content of the main products was under 8 w/w% applying the advantageous process parameters, even though the LCO content of the feedstocks. The cetane indexes of the main products changed between 48 and 50, their sulphur content was under 10 mg/kg until blending 10 % of WCO, in case of 15 % WCO content was still just 13 mg/kg. We concluded, that increasing the triglyceride content of feedstocks above 15 % is not recommended, because of the increased oxygen content the sulphur removal reactions are forced back. The cause of this is that the sulphur- and oxygen removal reactions are occuring on the same active sites of the catalyst, as well as the aromatic hydrogenation reactions, which are contributing to achieve the high degree of desulphurization.

Synthesis and 1-butene hydrogenation activity of platinum decorated bamboo-shaped multiwall carbon nanotubes

Bamboo-shaped carbon nanotubes (BCNT) were prepared from three different amines on supported iron (Fe) and nickel (Ni) catalysts by catalytic chemical vapor deposition. The main factors governing product morphology and defect site density were identified. Post-synthetic oxidative functionalization was used to add carboxyl groups to the nanotubes, and then platinum (Pt) nanoparticles were deposited on the surface by the in situ reduction of a platinum salt. The average Pt nanoparticle diameter was found to be affected by the extent of surface functionalization. The catalytic performance of the synthesized Pt/BCNT samples were examined in the hydrogenation of 1-butene, in order to show that the catalytic activity of the bamboo like carbon nanotube supported Pt catalyst is similar to the conventional Pt catalysts in heterogeneous catalytic hydrogenation. The best overall performance was achieved when the bamboo-shaped nanotube support was synthesized on 5 wt% Fe/Al(OH)3 catalyst from triethylamine and decorated with 5 wt% platinum nanoparticles.

Surface enhanced Raman spectroscopic (SERS) behavior of substituted propenoic acids used in heterogeneous catalytic asymmetric hydrogenation

The strength and geometry of adsorption of substituted propenoic acids on silver surface were studied by means of surface enhanced Raman spectroscopy (SERS) using silver sol. Based on their SERS behavior, two classes of phenylpropenoic acids studied were distinguished. The first class of propenoic acids (atropic acid, (E)‐2,3‐diphenylpropenoic acid, (E)‐2‐(2‐methoxyphenyl)‐3‐phenylpropenoic acid, (E)‐2,3‐di‐(4‐methoxyphenyl)phenylpropenoic acid and (E)‐2‐(2‐methoxyphenyl)‐3‐(4‐fluorophenyl)propenoic acid) has shown strong charge transfer (CT) effect. We suggest bidentate carboxyl bonded species based on the SERS enhanced bands of νCOO− around 1394 cm−1 and νC―C of the ―C―COO− moiety at 951 cm−1. In these series the plane of the α‐phenyl group (γCH out‐of‐plane vibrations at 850–700 cm−1) is almost parallel to the silver surface, while the β‐phenyl group is in tilted position depending on the type and the position of substituent(s) showing strong SERS enhanced bands of νCC + βCH (in‐plane mode) at 1075 cm−1, νCC (ring breathing mode, in‐plane) at 1000 cm−1 and γCCC (out‐of‐plane mode) around 401 cm−1. The other class of propenoic acids (cinnamic acid, (E)‐2‐phenyl‐3‐(4‐methoxyphenyl)propenoic acid) has shown weak electromagnetic (EM) enhancement (CC bands is enhanced in cinnamic acid). In this case no significant carboxyl enhancement was observed, so we suggest that adsorbed species lie parallel to the surface. The two types of adsorption can be related to the dissociation ability of the carboxylic group. In the first case the carboxylic H dissociates, while in the second case it does not, as indicated also by the characteristic νCO band at 1686 cm−1 in the FT‐Raman spectra of methanolic solutions. Copyright © 2015 John Wiley & Sons, Ltd.

DMF Dimethyl Acetal as Carbon Source for α-Methylation of Ketones: A Hydrogenation-Hydrogenolysis Strategy of Enaminones.

A novel heterogeneous catalytic hydrogenation-hydrogenolysis strategy has been developed for the α-methylation of ketones via enaminones using DMF dimethyl acetal as carbon source. This strategy provides a very convenient route to α-methylated ketones using a variety of ketones without any base or oxidant.

Liquid phase hydrogenation of nitrobenzene

Hydrogenation of nitrobenzene (NB) was carried out in methanol solutions (initial concentration 0.8moll−1) over a Pd/C catalyst (3wt.% of Pd; reaction mixture contained 2.2mgPdl−1) over the pressure range of 2–4MPa and temperature 30–70°C in a laboratory scale batch reactor. Zero order kinetics was observed at hydrogen pressures above 2MPa Under applied experimental conditions the apparent activation energy was 35±1kJmol−1. A detailed analysis of the reaction mixture inspired the hypothesis that a C6H5–NO(H) moiety is formed on the catalyst surface and it undergoes further condensation to azoxybenzene (AOB) releasing water. However, very low concentrations of azobenzene (AB) and hydrazobenzene (HAB) in the reaction mixture indicate that the reaction route to the formation of aniline by hydrogenation of AOB to AB, hydrazobenzene (HAB) and subsequent hydrogenolysis to AN is of low probability. Hydrogenolysis of AOB to C6H5–NO(H) and C6H5–N(H), where the latter is hydrogenated to AN, is more likely. Based on the experimental observations a new reaction scheme for the heterogeneous catalytic hydrogenation of NB was proposed.

Combination of Reaction and Separation in Heterogeneous Catalytic Hydrogenation of Ethylformate

AbstractContinuous hydrogenation reaction of ethyl benzoylformate was studied over a (–)‐cinchonidine (CD)‐modified Pt/Al2O3 catalyst. The catalyst showed a good stability, and high enantioselectivity was achieved in the fixed‐bed reactor. Chromatographic separation of (R)‐ and (S)‐ethyl mandelate originating from a post‐continuous hydrogenation reaction of ethyl benzoylformate over the (–)‐CD‐modified Pt/Al2O3 catalyst was investigated in the same reaction mixture. A commercial column filled with a chiral selector resin was chosen as a perspective preparative‐scale adsorbent. Since adsorption equilibrium isotherms were linear within the entire investigated range of concentrations, they were determined by pulse experiments for the isomers present in a post‐reaction mixture. Breakthrough curves were measured and described successfully by the dispersive plug‐flow model with linear driving force approximation.