Moderate Conversion Research Articles

Zr/P/O catalyst for the direct acid chemo-hydrolysis of non-pretreated microcrystalline cellulose and softwood sawdust

This paper compares the catalytic behavior of several heterogeneous acid catalysts in the direct hydrolysis of an untreated softwood dust. Among the various catalysts investigated, some were characterized by a relatively high yield to monosaccharides, such as a Zirconium phosphate and the reference Amberlyst 15. Conversely, some catalyst types, i.e. Sn/W mixed oxide and Zirconia-grafted trifluoromethanesulfonic acid, were selective into glucose, since sugars derived from hemicellulose dissolution and hydrolysis were rapidly degraded. A detailed analysis of the reactivity of Zr/P/O was conducted, in the hydrolysis of both untreated and ball-milled microcrystalline cellulose; at 150°C and 3h reaction time, the catalyst gave high selectivity to glucose, with negligible formation of 5-hydroxymethylfurfural, and moderate cellulose conversion. After cellulose ball-milling, a notable increase in conversion was achieved, still with a high selectivity to glucose and very low formation of degradation compounds. The catalyst showed high affinity for β-1,4-glucans, as demonstrated by the activity in cellobiose hydrolysis into glucose.

Recent advances in alternative cathode materials for iodine-free dye-sensitized solar cells

Over the last decades, iodine-free redox couples have been widely investigated as alternatives for the ubiquitous triiodide/iodide redox shuttle in dye-sensitized solar cells (DSCs). This is mainly motivated by desires to overcome the disadvantages associated with the latter, such as large energy loss in the dye regeneration process, visible light absorption and corrosiveness towards current-collecting metal grids. However, conventional Pt cathodes show poor catalytic activity towards those iodine-free redox couples, resulting in poor fill factors and relatively moderate power conversion efficiencies. The ultimate solution to address this challenge is to develop alternative economical Pt-free catalysts. This review selectively discusses and summarizes the recent advances in novel cathode materials for electrolytes free of iodine-based redox couples, mainly including inorganic transition metal compounds, organic conductive polymers and carbonaceous materials (particularly carbon nanotubes and graphene). Most of these advances have been realized by judiciously controlling the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, this review highlights the importance of matchup between catalysts and the redox couples, and points to crucial issues that should be addressed in the pursuit of developing low-cost and high-catalytic cathodes for DSCs.

Low band-gap donor–acceptor copolymers based on dioxocyclopenta[c]thiophene derivatives as acceptor units: synthesis, properties, and photovoltaic performances

New donor–acceptor type copolymers containing dihexyldioxocyclopenta[c]thiophene or (dihexylmethylidene)dioxocyclopenta[c]thiophene as acceptor units have been designed and synthesized for the application as hole-transporting (p-type) organic semiconducting materials in organic photovoltaics (OPVs). The investigation of photophysical and physicochemical properties revealed that these copolymers featured low optical band gaps (1.56–1.73 eV) and low-lying HOMO energy levels (−5.40 to −5.02 eV). Bulk heterojunction OPV devices based on these copolymers and [6,6]-phenyl-C61-butyric acid methyl ester as active layers showed moderate power conversion efficiencies (PCEs) of between 1.36 and 2.68% under air mass 1.5 simulated solar illumination. Space-charge-limited current measurements and atomic force microscopy measurements of the blend films revealed that both charge-transporting characteristics and film morphologies have significant influences on the photovoltaic performances. OPV devices based on the copolymers with [6,6]-phenyl-C71-butyric acid methyl ester showed a PCE of up to 5.17% with a short circuit current of 10.1 mA cm−2, an open circuit voltage of 0.80 V and a fill factor of 0.64.

Design and performance evaluation of a photovoltaic grid-connected system in hot weather conditions

A pilot photovoltaic (PV) grid-connected system rated at 36 kWp has been designed and installed at the 0.4 kV level of the Abu Dhabi distribution network. The performance of the system under the actual weather conditions has been evaluated in terms of power and energy production, conversion efficiency, consistency of voltage and frequency, along with the impact of ambient temperature. Additionally, the influence of accumulated dust deposition on the production of the PV array has been evaluated. The evaluation showed consistent operation of the system with a moderate conversion efficiency even with the high ambient temperatures at the site. However, the dust deposition on the glazing of PV modules was found to seriously degrade the performance of the PV system.The outcome of this work is deemed important in assisting accurate PV system design, and also in scheduling suitable cleaning cycles for the PV strings. In this regard, cleaning the strings on a monthly basis was found to give reasonable results.

Establishing the role of Brønsted acidity and porosity for the catalytic etherification of glycerol with tert-butanol by modifying zeolites

The role of Brønsted acidity and porosity for the etherification of glycerol with tert-butanol was studied by modifying the surface and acidic characteristics of three commercial Na-zeolites (mordenite, beta and ZSM-5) by protonation, dealumination, desilication-protonation, lanthanum-exchange and fluorination. Catalytic results can be related to the amount and strength of Brønsted acid sites together with the accessibility of the reactants to the acid sites. Modifications made on ZSM-5 did not affect considerably its surface and acidic properties, and consequently its catalytic behaviour, leading moderate conversion values and low/null selectivity to di- and tri-tertiary butyl ethers of glycerol (h-GTBE). Mordenite catalysts showed low conversion and moderate/low selectivity to h-GTBE due to the lower amount of acid centres, lower external surface area, more hydrophilic character and lower dimensionality of the mordenite structure when compared with the other two zeolites. Beta catalysts exhibited the best catalytic results. The introduction of fluorine in the beta zeolite framework generated higher amounts of stronger acid sites, which were able to transform glycerol until the glycerol triether. Thus, fluorinated beta yielded the best conversion (75%) and selectivity to h-GTBE (37%) with the formation of glycerol triether in low amounts. These values were comparable to those obtained at the same reaction conditions with an Amberlyst-15, an acid catalyst traditionally used for this reaction.

Ruthenium promotion of Co/SBA-15 catalysts for Fischer-Tropsch synthesis in slurry-phase reactors

The aim of this work was to evaluate the catalytic properties of a Ru promoted Co/SBA-15 catalyst for Fischer-Tropsch synthesis (FTS). The Ru promoted Co/SBA-15 catalyst was prepared by wet impregnation method and was characterized by X-ray diffraction, X-ray energy dispersion spectrophotometer, N2 adsorption-desorption, temperature-programmed reduction and transmission electron microscopy. The Fischer-Tropsch synthesis using the catalyst was carried out to evaluate the catalyst activity and its effect on FTS product distribution. The synthesis was carried out in a slurry reactor operating at 513 K, 20 atm, CO: H2 molar ratio of 1: 1. X-ray diffraction showed that the calcined cobalt catalyst did not modify the structure of SBA-15, proving that Co was present in the form of Co3O4 in the catalyst. The addition of cobalt in SBA-15 decreased the specific superficial area of the molecular sieve. Fischer-Tropsch synthesis activity and C5+ hydrocarbon selectivity increased with the addition of Ru. The increases in activity and selectivity were attributed to the increased number of active sites resulting from higher reducibility and the synergetic effect of Ru and Co. Ru/Co/SBA-15 catalysts showed moderate conversion (40%) and high selectivity towards the production of C5+ (80 wt%).

Heterogeneous amination of bromobenzene over titania-supported gold catalysts

Amination of bromobenzene with aniline was carried out on heterogeneous Au–TiO2 catalysts prepared using the deposition–precipitation method. The deposition of gold in loadings in the range 0.1–0.9wt.% on titania occurred with the formation of gold particles with controlled size and oxidation state as demonstrated from TEM and XPS measurements. In addition, Raman and DR–UV–Vis investigation of these catalysts showed that the interaction of Au particles with the support stabilized the metallic state of gold. Catalytic results demonstrated that the conversion and selectivity depended on the gold-particle size and dispersion, while the mechanism of reaction was in direct relation with the reaction medium. Working in DMC, the solvent was playing the role of base. The advantage of working in DMC was avoiding the formation of KBr which is very difficult to be separated from the reaction products. HBr resulted as a by-product formed adducts with the coupling product, which was separated as crystals at room temperature by a simple filtration. However, in DMC, the reaction occurred with low selectivities. In dioxane, the presence of potassium ethoxide as base was mandatory. The reaction occurred with very high selectivities for moderate conversions. The conversion was limited by KBr released from the reaction. However, the use of the heterogeneous catalyst has the advantage of scavenger, since KBr becomes chemisorbed on the surface and could be simple removed by percolation and the catalyst can be reused.

Cross‐metathesis versus palladium‐catalyzed CH activation: Acetoxy ester functionalization of unsaturated fatty acid methyl esters

AbstractTwo synthetic approaches to functionalize plant oil derived platform chemicals were investigated. For this purpose, methyl 10‐undecenoate, which can be obtained by pyrolysis of castor oil, was used in olefin cross‐metathesis under neat conditions forming an unsaturated α,ω‐acetoxy ester. A catalyst screening with 11 different ruthenium‐based metathesis catalysts was performed, revealing that well‐suited catalysts allow for full conversion and very good cross‐metathesis selectivity at a loading of only 0.5 mol%. An alternative possibility to the aforementioned synthetic method is a palladium‐catalyzed reaction of methyl 10‐undecenoate with acetic acid in the presence of dimethyl sulfoxide. Here, the formation of linear and branched unsaturated acetoxy esters as well as a ketone was observed. The conversion as well as the selectivity of this procedure was studied under different reaction conditions and compared to the cross‐metathesis results. Based on the successful functionalization of methyl 10‐undecenoate, methyl oleate was investigated in this palladium‐catalyzed CH activation reaction. Due to the lower reactivity of the internal double bond the desired acetoxy ester was only obtained in moderate conversion in this case. In summary, this study clearly shows that palladium‐catalyzed functionalization of unsaturated fatty compounds via CH activation is an attractive alternative to the well‐established olefin cross‐metathesis procedure.

Structure–Activity Studies on Highly Active Palladium Hydrogenation Catalysts by X-ray Absorption Spectroscopy

Functionalized carbon nanotubes were used to produce Pd-based hydrogenation catalysts. Pd/CNT with small (1–2 nm) Pd particles showed classical catalytic behavior in propyne hydrogenation, with high propene selectivity at moderate conversion levels and propane formation near full conversion. Pd/CNT with larger (∼15 nm) nanoparticles, however, was selective (88%) toward propene even at practically full propyne conversion. An additionally prepared Pd2Ga/CNT catalyst exhibited even higher propene selectivity at full conversion. All of these materials were studied in situ by X-ray absorption spectroscopy at the Pd K-edge. Pd2Ga/CNT was stable under all conditions examined without variation in XANES or in the derived EXAFS parameters. Both Pd/CNT samples formed β-hydride under hydrogen, as assessed from the calculated lattice expansion and the characteristic red shift of the XANES maxima. The minor spectroscopic difference between the monometallic catalysts observed at high propyne conversion suggests the decisive role of a Pd–C (subsurface C) contribution in the structure of larger Pd particles, being absent with ultrasmall nanoparticles. In general, all factors (intermetallic phase formation, subsurface C, etc.) that reduce the surface H coverage will give rise to enhanced partial hydrogenation selectivity of palladium when secondary alkene hydrogenation at late bed segments or diffusion issues in the pores are avoided.

Buckminsterfullerene derivatives bearing a fluoroalkyl group for use in organic photovoltaic cells

Six novel fluoroalkylpyrrolidine-substituted [60]fullerene derivatives were synthesized and their ability to perform as new n-type organic photovoltaic materials was evaluated. The fullerene derivatives were soluble in common organic solvents, affording good processability properties for the fabrication of photovoltaic cells, and showed an absorption range and molar extinctions similar to those of [6,6]-phenyl C61 butyric acid methyl ester. Bulk-heterojunction photovoltaic cells using poly(3-hexylthiophene):fullerene derivative blends as the photovoltaic active layers were fabricated and characterized. The performances of the photovoltaic cells were notably affected by the substituents on the fullerene derivatives. Short fluoroalkyl (C4F9) chains on pyrrolidine-linked phenyl groups were suitable substituents for the photovoltaic materials in the current study. This fullerene derivative bearing a C4F9-phenyl group showed a moderate power conversion efficiency of 0.53% during simulated AM 1.5G solar irradiation at 100mW/cm2. This is so far the first report of the use of fluoroalkyl fullerene derivatives as the active materials in organic photovoltaic cells.

The influence of conventional heating and microwave irradiation on the resolution of (RS)-sec-butylamine catalyzed by free or immobilized lipases

The lipases CAL-B, PSL, PSL-C, PSL-D, and A. niger lipase, free or immobilized in starch (obtained from two types of yam, known in Brazil as “cara” (Discorea alata L.) and “inhame” (Colocasia esculenta (L.) Schott) or gelatin films, were used in the acylation of (RS)-sec-butylamine with different acyl donors in various organic solvents applying conventional heating (CH) or microwave (MW) irradiation. In the case of free A. niger lipase, the conversion degrees were three times higher using MW irradiation when compared to conventional heating at 35 oC. Using free A. niger lipase, the (R)-amide was obtained with a conversion degree of 21%, resulting in eep > 99% and E-value (enantioselectivity value) > 200, in 1 min of reaction under MW irradiation. When the A. niger lipase was immobilized in yam starch films, the (R)-amide was obtained in moderate conversions of 8-25% after 3 or 5 min of reaction under MW irradiation, but with higher selectivity (eep > 99% and E > 200) in comparison with the free form (conversion degree of 45%, eep 81% and E value of 18).

Upgrading of Fischer–Tropsch synthesis bio-waxes via catalytic cracking: Effect of acidity, porosity and metal modification of zeolitic and mesoporous aluminosilicate catalysts

The development of novel catalytic processes for the upgrading of F–T waxes towards the production of clean transportation fuels as well as other valuable gaseous alkenes in the overall Biomass-to-Liquid (BTL) process would increase the sustainability of this growing technology significantly. Recent studies have shown that an alternative to the classical hydrocracking process for the upgrading of heavy waxy hydrocarbons could be the Fluid Catalytic Cracking (FCC) process, which aims mainly to the production of gasoline and gaseous (C3, C4) alkenes. In the present work, we have used “model” zeolitic and mesoporous aluminosilicate catalytic materials that exhibit different acidic and porosity characteristics, in order to elucidate the reaction mechanism of F–T wax cracking and to identify the effects of these catalyst properties on conversion and product yields. In addition, the effect of moderating the acidity of zeolites via steaming (in analogy to commercial FCC equilibrated catalysts) or by using alkaline metals that block the acid sites and the effect of using specific metals with dehydrogenation activity, have also been studied. It was shown that the Brönsted zeolitic acid sites, mainly the ones of higher strength, are responsible for the high cracking activity of the heavy paraffinic feed, while the Lewis acid sites contributed to a lesser extent. Furthermore, the different micropore structure/size of zeolites Y, ZSM-5 and Beta had a significant effect on conversion and product yields (C2–C4 gases, gasoline, LCO, coke), as well as on gasoline composition (PIONA) and octane number (RON/MON). The mildly acidic amorphous mesoporous aluminosilicates exhibited moderate conversion and different product yields and gasoline composition, compared to zeolites. The catalytic results of the present study were rationalized on the basis of well-established reaction mechanisms for n-paraffins cracking on zeolites, and can be utilized for the design of new cracking catalysts with tailored catalytic properties in F–T wax upgrading.

Immobilization of marine fungi on silica gel, silica xerogel and chitosan for biocatalytic reduction of ketones

Abstract The scanning electron microscopy (SEM) analysis showed that whole living hyphal of marine fungi Aspergillus sclerotiorum CBMAI 849 and Penicillium citrinum CBMAI 1186 were immobilized on support matrices of silica gel, silica xerogel and/or chitosan. P. citrinum immobilized on chitosan catalyzed the quantitative reduction of 1-(4-methoxyphenyl)-ethanone ( 1 ) to the enantiomer (S)-1-(4-methoxyphenyl)-ethanol ( 3b ), with excellent enantioselectivity ( ee > 99%, yield = 95%). Interestingly, ketone 1 was reduced with moderate selectivity and conversion to alcohol 3b ( ee = 69%, c 40%) by the free mycelium of P. citrinum . This free mycelium of P. citrinum catalyzed the production of the ( R )-alcohol 3a , the antipode of the alcohol produced by the immobilized cells. P. citrinum immobilized on chitosan also catalyzed the bioreduction of 2-chloro-1-phenylethanone ( 2 ) to 2-chloro-1-phenylethanol ( 4a,b ), but in this case without optical selectivity. These results showed that biocatalytic reduction of ketones by immobilization hyphal of marine fungi depends on the xenobiotic substrate and the support matrix used.

Catalytic activity of metal organic framework Cu3(BTC)2 in the cycloaddition of CO2 to epichlorohydrin reaction

We demonstrate the novel, catalytic activity of metal organic framework of Cu3(BTC)2 catalysts in the synthesis of chloropropene carbonate from CO2 and epichlorohydrin. The catalysts display moderate epoxide conversions, and moderate selectivities to chloropropene carbonate at 100°C. No solvents or co-catalysts were required. It is suggested that Lewis acid copper (II) sites in the Cu3(BTC)2 framework promoted the adsorption of carbon dioxide on the solid surface and its further conversion to the carbonate.

Synthesis of Juglone (5-Hydroxy-1,4-Naphthoquinone) in a Falling Film Microreactor

Photooxygenation of 1,5-dihydroxynaphthalene to Juglone was studied in a falling film microreactor. Moderate conversion rates of up to 31% were achieved after just 160 s of exposure to visible light. In contrast, batch reactions gave much lower conversions of up to 14% after a prolonged time period of 10 min. The difference in performance is explained by the superior light penetration in the microfilm and the large gas-liquid contact area.

Rapid catalyst evaluation for Sonogashira coupling in continuous flow

Selection of the most appropriate catalyst for Pd-catalyzed Sonogashira coupling often requires time and resources. We applied a continuous flow device for rapid catalyst screening of 4 heterogeneous catalysts over 6 Sonogashira coupling reactions together with longevity estimation. The screening procedure requires only 8 hours. For coupling the alkynes with 4- iodo-anisole Fibrecat types of catalysts showed the highest performance, while when 4-bromo- anisole was applied as an aromatic halide PdCl2(PPh3)2 DVB gave superior results. For phenyl- acetylene and ethynyl-cyclohexene the coupling of the bromo derivative resulted in relatively low conversion as well as selectivity for most of the polymer-bound catalysts. Applying the cheap catalyst 10 % Pd/C the coupling reaction could only be achieved with the rather reactive 4- iodo-anisole although with moderate conversion.

Improved Photovoltaic Performance of a Semicrystalline Narrow Bandgap Copolymer Based on 4H-Cyclopenta[2,1-b:3,4-b′]dithiophene Donor and Thiazolo[5,4-d]thiazole Acceptor Units

A solution processable narrow bandgap polymer composed of alternating 2,5-dithienylthiazolo[5,4-d]thiazole and asymmetrically alkyl-substituted 4H-cyclopenta[2,1-b:3,4-b′]dithiophene units (PCPDT-DTTzTz) was synthesized by Suzuki polycondensation and the donor–acceptor copolymer was thoroughly characterized. Thermal analysis and X-ray diffraction studies disclosed the semicrystalline nature of the material. When blended with PC71BM and integrated in bulk heterojunction organic solar cells, a moderate power conversion efficiency of 2.43% under AM 1.5 G (100 mW/cm2) conditions was obtained. However, upon purification of the semiconducting copolymer by preparative size exclusion chromatography, a noticeable rise in power conversion efficiency to 4.03% was achieved. The purified polymer exhibited a relatively high field-effect carrier mobility of 1.0 × 10–3 cm2/(V s). The active layer morphology was explored by atomic force microscopy and transmission electron microscopy studies, showing phase segregation on the nanometer scale.

Dye Sensitized Solar Cells: A Review

The development of dye sensitized solar cells (DSSCs), which have derived inspiration from photosynthesis, has opened up exciting new possibilities and paradigms for producing solar photovoltaics possibly at lower cost. The dye-sensitized solar cells with moderate power conversion (∼10%) efficiencies can be manufactured under regular lab conditions without needing clean rooms or very specialized facilities. The entire processing need not involve even a single vapour deposition step. The DSSCs can be considered to be electrochemical devices consisting of (a) a photoanode which has a thick film of a wide band gap oxide semiconductor (like TiO2), typically coated on a transparent conductive oxide (TCO) glass substrate, with TiO2 being sensitized with adsorbed dyes that absorb visible light, (b) an electrolyte that establishes the internal electrical continuity between anode and counter electrode and mainly plays the role of regenerating the dye such that the photoexcitation, electron injection and current flow continues, (c) the counter electrode which is also usually a TCO coated transparent substrate with a suitable catalytic material deposited over it to facilitate efficient charge (electron) transfer from external connection to the electrolyte, (d) sealants to seal the cell assembly containing the electrolyte and prevent ingress of atmospheric influences that may interfere with functioning of the DSSC. The present review describes research that has been carried out and continues on various aspects of DSSCs including developing greater understanding of the basic mechanisms involved, use of new materials, processing techniques and their impact on performance of the cells. A number of challenges are yet to be overcome to realize commercialization of the DSSCs which appears imminent in the near future.

Role Transition from Mental Health Nurse to IAPT High Intensity Psychological Therapist

The Improving Access to Psychological Therapies (IAPT) initiative has depended on the training of a new NHS mental health workforce. At step 3 of the stepped care model, capacity building has required the recruitment of a wide range of mental health professionals into high intensity therapists training posts. This shift naturally entails role transition on the part of trainees into delivering cognitive behavioural psychotherapy (CBP), but no previous research has examined the experience of such transitions. To describe the lived experience of transition from mental health nurse to IAPT high intensity therapist and to identify possible factors which moderate effective role conversions. Six qualified high intensity therapists were interviewed using a semi-structured interview and the subsequent interviews transcribed. Thematic content analysis (TCA) was used to analyze personal accounts of role transition. All participants had previously been mental health nurses and attended the same IAPT high intensity therapist (HIT) training programme. Six key themes were apparent from the TCA. Three interconnected themes concerning supervision (style, impact of approach and historical context) and three additional themes of the challenge of learning a new clinical approach, high need for support, and forming a new psychotherapist identity. Findings suggest supervision is the most important factor in supporting complex psychotherapy role transitions. Clinical supervisors may need to incorporate dedicated time on role and identity shift during CBP training to ensure effective assimilation and transition. Methodological short-comings are identified and discussed.

Oxidative dehydrogenation of lower alkanes over metal incorporated MCM-41 catalysts

Abstract A series of metal incorporated M-MCM-41 (M = Ce, Mo, and/or V) mesoporous materials were synthesized by the hydrothermal method. The synthesized mesoporous materials were characterized by the XRD, BET, TPR and EPR techniques. The extent of mesoporous structural ordering was evident from the XRD pattern of M-MCM-41. The catalytic properties of the metal containing MCM-41 catalysts were evaluated for oxidative dehydrogenation of propane and n-butane in a fixed-bed micro-reactor. The results showed higher activity in case of V-MCM-41 catalyst as compared to that of Mo-MCM-41 catalysts over a temperature range of 500–600 °C at atmospheric pressure. Cerium containing MCM-41 catalyst showed high selectivity (78%) for butadiene at moderate conversion of about 4%. The major products include ethylene, propylene and butanes. Propane conversion of about 20% with corresponding propylene selectivity of around 30% was obtained at 575 °C over V-MCM-41 catalyst. A small amount of H2 besides COx was also produced...