Catalysts, Volume 6, Issue 11 (November 2016) – 15 articles

The catalyst layers for polymer-electrolyte-membrane (PEM) fuel cells were fabricated by deposition of platinum directly onto the gas diffusion layer using pulsed laser deposition (PLD). This technique reduced the number of steps required to synthesize the catalyst layers and the amount of Pt loading required. PEM fuel cells with various Pt loadings for the cathode were investigated. With a cathode Pt loading of 100 $\mathsf{\mu }$ g·cm ${}^{-2}$ , the current density of a single cell reached 1205 mA·cm ${}^{-2}$ at 0.6 V, which was close to that of a single cell using an E-TEK (trademark) Pt/C electrode with a cathode Pt loading of 400 $\mathsf{\mu }$ g·cm ${}^{-2}$ . Furthermore, for a PEM fuel cell with both electrodes prepared by PLD and a total anode and cathode Pt loading of 117 $\mathsf{\mu }$ g·cm ${}^{-2}$ , the overall Pt mass-specific power density at 0.6 V reached 7.43 kW·g ${}^{-1}$ , which was five times that of a fuel cell with E-TEK Pt/C electrodes. The high mass-specific power density was due to that a very thin nanoporous Pt layer was deposited directly onto the gas diffusion layer, which made good contact with the Nafion membrane and thus resulted in a low-resistance membrane electrode assembly. Full article

To prevent sintering, ozone treatment at mild temperature is used to remove the capping agent from supported Au nanoparticles. The Au nanoparticles are first synthesized as a colloidal solution and then supported on alumina. Fourier Transform Infra Red (FTIR) shows the capping agent is removed completely. Transmission Electron Microscopy (TEM) and catalytic test reactions show the Au does not sinter significantly upon low temperature ozone treatment. Full article

In the last twenty years, N-heterocyclic carbenes (NHCs) have acquired considerable popularity as ligands for transition metals, organocatalysts and in metal-free polymer synthesis. NHCs are generally derived from azolium based salts NHCH⁺X⁻ by deprotonation or reduction (chemical or electrochemical) of NHCH⁺. The extensive knowledge of the physicochemical properties of NHCH⁺/NHC system could help to select the conditions (scaffold of NHC, nature of the counter-ion X⁻, solvent, etc.) to enhance the catalytic power of NHC in a synthesis. The electrochemical behavior of NHCH⁺/NHC system, in the absence and in the presence of solvent, was extensively discussed. The cathodic reduction of NHCH⁺ to NHC and the anodic oxidation of NHC, and the related effect of the scaffold, solvent, and electrodic material were emphasized. The electrochemical investigations allow acquiring further knowledge as regards the stability of NHC, the acidic and nucleophilic properties of NHCH⁺/NHC system, the reactivity of NHC versus carbon dioxide and the effect of the hydrogen bond on the catalytic efficiency of NHC. The question of the spontaneous or induced formation of NHC from particular ionic liquids was reconsidered via voltammetric analysis. The results suggested by the classical and the electrochemical methodologies were compared and discussed. Full article

In order to design improved chiral ruthenium catalysts for asymmetric olefin metathesis, enantiomeric catalysts incorporating C₁-symmetric N-Heterocyclic carbenes (NHC) ligands with syn-related substituents on the backbone were synthesized starting from meso-1,2-diphenylethylenediamine. The absolute configuration of the enantiomers of the desymmetrized meso diamine was assigned by optical rotation analysis and in silico calculations, and was found to be maintained in their respective ruthenium catalysts by comparison of the relative electronic circular dichroism (ECD) spectra. The catalytic behaviour of the enantiomeric ruthenium complexes was investigated in model asymmetric metathesis transformations and compared to that of analogous complexes bearing C₁-symmetric NHC ligands with an anti backbone. Modest enantioselectivities were registered and different catalyst properties depending on the nature of stereochemical relationship of substituents on the backbone were observed. Full article

Performances of bimetallic catalysts (Ni-Co) supported on different acidic carriers (HZSM-5, HBeta, HY, ZrO₂) and corresponding monometallic Ni catalysts in aqueous phase hydrodeoxygenation of phenol were compared in batch and continuous flow modes. The results revealed that the support acidity plays an important role in deoxygenation as it mainly controls the oxygen-removing steps in the reaction network. At the same time, sufficient hydrothermal stability of a solid catalyst is essential. Batch experiments revealed 10Ni10Co/HZSM-5 to be the best-performing catalyst in terms of conversion and cyclohexane yield. Complementary continuous runs provided more insights into the relationship between catalyst structure, efficiency and stability. After 24 h on-stream, the catalyst still reveals 100% conversion and a slight loss (from 100% to 90%) in liquid hydrocarbon selectivity. The observed alloy of Co with Ni increased dispersion and stability of Ni-active sites, and combination with HZSM-5 resulted in a well-balanced ratio of metal and acid sites which promoted all necessary steps in preferred pathways. This was proved by studies of fresh and spent catalysts using various characterization techniques (N₂ physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and infrared spectroscopy of adsorbed pyridine (pyr-IR)). Full article

Selected results for the synthesis of cyclic olefin copolymers (COCs)—especially copolymerizations of norbornene (NBE) or tetracyclododecene (TCD) with ethylene and α-olefins (1-hexene, 1-octene, 1-dodecene)—using group 4 transition metal (titanium and zirconium) complex catalysts have been reviewed. Half-titanocenes containing an anionic ancillary donor ligand, Cp’TiX₂(Y) (Cp’ = cyclopentadienyl; X = halogen, alkyl; Y = anionic donor ligand such as aryloxo, ketimide, imidazolin-2-iminato, etc.), are effective catalysts for efficient synthesis of new COCs; ligand modifications play an important role for the desired copolymerization. These new COCs possess promising properties (high transparency, thermal resistance (high glass transition temperature), low water absorption, etc.), thus it is demonstrated that the design of an efficient catalyst plays an essential role for the synthesis of new fine polyolefins with specified properties. Full article

In this work, poly(n-butylamino)(allylamino)phosphazene (PBAP) was synthesized and tethered on polypropylene microporous membrane (PPMM) with the aim of offering a biocompatible and, at the same time, moderately hydrophobic microenvironment to lipase for the first time. Lipase from Candida rugosa was used and the influence of membrane surface conditions on the activities of immobilized lipases was evaluated. Water contact angle measurement as well as field emission scanning electron microscopy were used to characterize the morphology of the modified membranes. The results showed an improvement in the adsorption capacity (26.0 mg/m²) and activity retention (68.2%) of the immobilized lipases on the PBAP-modified PPMM. Moreover, the lipases immobilized on the modified PPMM showed better thermal and pH stability. Full article

Ru is considered as an effective active species for N₂O decomposition; however, there is disagreement about which ruthenium species is key for catalytic activity. In order to understand the role of Ru species in N₂O decomposition, Ru/Al₂O₃ (Ru/Al₂O₃-H₂, Ru/Al₂O₃-NaBH₄, Ru/Al₂O₃-air) catalysts with different ratios of metallic Ru were prepared and evaluated for their catalytic activities. Various characterizations, especially in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), were applied to investigate the relationship between activity and different Ru species. The results indicate that the N₂O conversion displayed a linear relationship with the amount of metallic Ru. The DRIFTS results of adsorption for N₂O show that metallic Ru was the active site. The catalytic processes are put forward based on metallic Ru species. The deactivation with increasing times used is due to the decrease in the amount of metallic Ru and agglomerates of Ru particles on the surface of catalysts. Full article

In this research, catalytic steam reforming of acetic acid derived from the aqueous portion of bio-oil for hydrogen production was investigated using different Ni/ATC (Attapulgite Clay) catalysts prepared by precipitation, impregnation and mechanical blending methods. The fresh and reduced catalysts were characterized by XRD, N₂ adsorption–desorption, TEM and temperature program reduction (H₂-TPR). The comprehensive results demonstrated that the interaction between active metallic Ni and ATC carrier was significantly improved in Ni/ATC catalyst prepared by precipitation method, from which the mean of Ni particle size was the smallest (~13 nm), resulting in the highest metal dispersion (7.5%). The catalytic performance of the catalysts was evaluated by the process of steam reforming of acetic acid in a fixed-bed reactor under atmospheric pressure at two different temperatures: 550 °C and 650 °C. The test results showed the Ni/ATC prepared by way of precipitation method (PM-Ni/ATC) achieved the highest H₂ yield of ~82% and a little lower acetic acid conversion efficiency of ~85% than that of Ni/ATC prepared by way of impregnation method (IM-Ni/ATC) (~95%). In addition, the deactivation catalysts after reaction for 4 h were analyzed by XRD, TGA-DTG and TEM, which demonstrated the catalyst deactivation was not caused by the amount of carbon deposition, but owed to the significant agglomeration and sintering of Ni particles in the carrier. Full article

A series of vanadia catalysts supported on SBA-15 (V/SBA) with a vanadia (V) content ranging from 1% to 11% were prepared by an incipient wetness method. Their catalytic behavior in the dehydrogenation of isobutane to isobutene with CO₂ was examined. The catalysts were characterized by N₂ adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and temperature-programmed reduction (TPR). It was found that these catalysts were effective for the dehydrogenation reaction, and the catalytic activity is correlated with the amount of dispersed vanadium species on the SBA-15 support. The 7% V/SBA catalyst shows the highest activity, which gives 40.8% isobutane conversion and 84.8% isobutene selectivity. The SBA-15-supported vanadia exhibits higher isobutane conversion and isobutene selectivity than the MCM-41-supported one. Full article

LaNi₅, known for its hydrogen storage capability, was adapted to the form of a metal oxide-supported (γ-Al₂O₃) catalyst and its performance for the Sabatier reaction assessed. The 20 wt % La-Ni/γ-Al₂O₃ particles were prepared via solution combustion synthesis (SCS) and exhibited good catalytic activity, achieving a CO₂ conversion of 75% with a high CH₄ selectivity (98%) at 1 atm and 300 °C. Characteristics of the La-Ni/γ-Al₂O₃ catalyst were identified at various stages of the catalytic process (as-prepared, activated, and post-reaction) and in-situ DRIFTS was used to probe the reaction mechanism. The as-prepared catalyst contained amorphous surface La–Ni spinels with particle sizes <6 nm. The reduction process altered the catalyst make-up where, despite the reducing conditions, Ni²⁺-based particles with diameters between 4 and 20 nm decorated with LaO_x moieties were produced. However, the post-reaction catalyst had particle sizes of 4–9 nm and comprised metallic Ni, with the LaO_x decoration reverting to a form akin to the as-prepared catalyst. DRIFTS analysis indicated that formates and adsorbed CO species were present on the catalyst surface during the reaction, implying the reaction proceeded via a H₂-assisted and sequential CO₂ dissociation to C and O. These were then rapidly hydrogenated into CH₄ and H₂O. Full article

The Pd(TFA)₂-catalyzed [4+1] annulation of chained or cyclic α-alkenyl-dicarbonyl compounds and unprotected primary amines for “one-pot” synthesis of pyrroles is reported here. Enamination and amino-alkene were involved in this practical and efficient tandem reaction. The annulation products were isolated in moderate to excellent yields with O₂ as the terminal oxidant under mild conditions. In addition, this method was applied to synthesize highly regioselective aminomethylated and di(1H-pyrrol-3-yl)methane products. Full article

The microbial production of d-lysine has been of great interest as a medicinal raw material. Here, a two-step process for d-lysine production from l-lysine by the successive microbial racemization and asymmetric degradation with lysine racemase and decarboxylase was developed. The whole-cell activities of engineered Escherichia coli expressing racemases from the strains Proteus mirabilis (LYR) and Lactobacillus paracasei (AAR) were first investigated comparatively. When the strain BL21-LYR with higher racemization activity was employed, l-lysine was rapidly racemized to give dl-lysine, and the d-lysine yield was approximately 48% after 0.5 h. Next, l-lysine was selectively catabolized to generate cadaverine by lysine decarboxylase. The comparative analysis of the decarboxylation activities of resting whole cells, permeabilized cells, and crude enzyme revealed that the crude enzyme was the best biocatalyst for enantiopure d-lysine production. The reaction temperature, pH, metal ion additive, and pyridoxal 5′-phosphate content of this two-step production process were subsequently optimized. Under optimal conditions, 750.7 mmol/L d-lysine was finally obtained from 1710 mmol/L l-lysine after 1 h of racemization reaction and 0.5 h of decarboxylation reaction. d-lysine yield could reach 48.8% with enantiomeric excess (ee) ≥ 99%. Full article

Nano size Copper (Cu) incorporated TiO₂ nanotubes was successfully synthesized via the anodic oxidation technique in ethylene glycol (EG) containing 0.5 wt % NH₄F and 1.6 wt % KOH for the photocatalytic degradation of Simazine (2-chloro-4, 6-diethylamino-1,3,5-triazine) under Ultraviolet (UV) illumination. In the present study, the influence of different loading Cu concentrations on the formation of Cu-TiO₂ nanotubes film towards the photocatalytic degradation of Simazine is reported. Based on our study, it was found that the optimum Cu loading concentration was about 0.45 wt % on TiO₂ nanotubes film for approximately 64% photocatalytic degradation of Simazine after 4 h under UV illumination. This finding was mainly attributed to the uniform surface covering of the Cu loaded TiO₂NTs which acted as electron traps, preventing the recombination of electron hole pairs, eventually leading to higher photocatalytic activity of our photocatalyst in degrading the targeted organic pollutant, Simazine. Moreover, an increased kinetic rate of the degradation to 0.0135 h⁻¹ was observed in the presence of Cu in TiO₂NTs. Full article

A heme-dependent peroxidase (HDP) catalyzes the ortho-hydroxylation of l-tyrosine to l-3,4-dihydroxyphenylalanine (l-DOPA) in the presence of hydrogen peroxide. l-DOPA can be used for the treatment of Parkinson's disease. In this work, to improve the catalytic efficiency, the heme-dependent peroxidase has been genetically modified with an elastin-like polypeptide (ELP). bicinchoninic acid (BCA) assay demonstrated that HDP-ELP has a higher solubility in aqueous solutions than HDP. Circular dichroism (CD) spectra showed that HDP-ELP has a higher stability than HDP. Enzyme kinetics has been investigated over a range of substrate concentrations. It has been demonstrated that HDP-ELP exhibited a catalytic efficiency 2.4 times that of HDP. Full article