Pyridine Bases Research Articles

Synthesis of 3-picoline from acrolein dimethyl acetal and ammonia over NH4F-HF treated ZSM-5

The post-treated ZSM-5 was an effective catalyst for the synthesis of pyridine bases and therefore selecting suitable post-synthetic method was very crucial. In this work, a series of Mg-modified ZSM-5 with different forms was directly treated by HF-NH4F mixture solution, and then they acting as catalysts were for the first time employed for the reaction of acrolein dimethyl acetal, water and ammonia toward 3-picoline. The catalysts were characterized by means of XRD, SEM, EDX, FT-IR, 27Al MAS NMR, N2-physisorption, NH3-TPD and Py-IR techniques. The characterization results revealed that the fluorination had a great influence on the pore structure and acidity of catalysts, deriving from the simultaneous desilication and dealumination. These factors resulted in large changes on the catalytic activities toward the modified catalysts than the corresponding to parent ones.

The Role of Hydrogen Bonding in Proton-Coupled Electron Transfer. It Does Not Have to be Concerted Pcet: The Case of Phenylenediamines and Pyridines in Acetonitrile

Proton transfer often accompanies electron transfer in organic redox couples due to the large changes in acidity or basicity that result from oxidation or reduction. Classically, the overall reaction is thought to occur in two separate steps, either proton transfer followed by electron transfer, PT-ET, or electron transfer followed by proton transfer, ET-PT. More recently it has become abundantly apparent that a third option is also possible in which the proton and electron move together in a single kinetic step. This is concerted proton-electron transfer, CPET, and is generally believed to occur within a H-bonded intermediate. It is straightforward to show that E° of this step will have a value in between the E° values corresponding to the oxidation of the fully protonated and fully deprotonated forms. Experimental evidence for CPET is typically the observance of a significant deuterium isotope effect for the apparent one electron transfer. However, it is important to note that the electron-proton transfer does not have to be concerted within the H-bond complex. It could also occur step-wise. If slow electron transfer occurred followed by rapid proton transfer within the H-bond complex, no significant deuterium isotope effect would be expected, yet, at the same time, the overall reversibility of the electron-proton transfer would still be aided by providing a mechanistic pathway through the H-bond complex with its intermediate E°. We believe that the second oxidation of a simple phenylenediamine, H2PD, in the presence of pyridines in acetonitrile provides a nice example of the significant role that step-wise electron-proton transfer within a H-bond intermediate can play. Without added base, the second oxidation corresponds to the reversible one electron oxidation of the radical cation, H2PD+, to the quinoidal dication, H2PD2+. CV data in the presence of one equivalent of pyridines of different basicity result in a significant negative shift in the E1/2 of the second CV wave with no loss in reversibility. Continued addition of the pyridine leads to smaller incremental shifts with still no change in reversibility. Analysis of the observed E1/2’s with one equivalent pyridine as a function of pyridine basicity indicates that, even with the weakest base, proton transfer to the pyridine occurs. This interpretation is supported by spectroelectrochemical data. Thus, the overall reaction occurring in the second CV wave is H2PD+ + B = HPD+ + HB+ + e-, where B is the pyridine base and HB+ is its conjugate acid. The shifts in E1/2 upon further additions of pyridine are nicely predicted by the Nernst equation with this as the overall reaction. However, attempts to simulate the CV data with just PT and ET steps fail at the higher concentrations of pyridine. This is because the rate of the ET step becomes exceedingly slow as the base concentration increases and the thermodynamic potential becomes increasingly removed from the E° of the actual ET step. This issue is simply solved by including in the mechanism the possibility of electron transfer occurring through the H-bond intermediate. This simple change leads to good fits to the experimental data, providing solid support for such a H-bonding intermediate being involved. However, a comparison of experiments with 10:1 cyanopyridine: H2PD run in 2% CH3OH to those run in 2% CD3OD show no significant difference in the ΔEp of the second oxidation, providing no evidence for the oxidation involving CPET. Thus, it appears that ET-PT within the H-bond complex still greatly aids the reversibility of the reaction even without CPET.

Evaluating the Roles of Proton Transfer and H-Bonding in the Electron Transfer Reactions of Organic Redox Couples in Non-Aqueous Solvents: Oxidation of Phenylenediamines in the Presence of Pyridine Bases in Acetonitrile

Oxidation or reduction of organic redox couples typically leads to large changes in acidity or basicity, withthe result that proton transfer often accompanies electron transfer, particularly in aqueous solution. In lesspolar organic solvents, H-bonding also can play an important role. While it is generally appreciated thatproton transfer will have a greater effect on the overall reaction than H-bonding, it is not always straightforward to distinguish between the two, and, despite a considerable amount of research, a complete,quantitative understanding of the relative roles that the two play in the voltammetry that is observed uponaddition of acids or bases to organic redox couples in non-aqueous solution remains elusive. This study focuses on the electrochemistry of p-tetramethylphenylenediamine, H 2 PD, in acetonitrile in thepresence of pyridine bases. In acetonitrile, this compound undergoes a reversible one electron oxidationto the radical cation, H 2 PD + , followed by a second reversible oxidation to the strongly acidic quinoidaldication, H 2 PD 2+ . With the addition of 1 equivalent of the pyridine base, no significant change in the firstoxidation is observed, but there is a large negative shift in the E 1/2 of the second oxidation with no loss inreversibility. Subsequent additions show a smaller, incremental negative shift, still with no loss inreversibility. We believe that this behavior signals proton transfer is occurring between the pyridine, pyr,and the H 2 PD 2+ , so that the overall reaction occurring in the second oxidation corresponds to H 2 PD + + pyr= HPD + + Hpyr + + e-. In this case, the observed E 1/2 should depend linearly on the pK a of the Hpyr + with aslope of −60 mV/pH unit. To test this hypothesis, the voltammetry of H 2 PD was studied with differentpyridines that cover a range of pK a values. A plot of E 1/2 of the wave observed with 1 eq pyridine vs. pKa isindeed linear with close to the predicted slope. Furthermore, it is found that the continued shift in E 1/2 ofthe second oxidation with increasing concentrations of pyridine is well-accounted for simply by applyingthe Nernst equation to the overall reaction. However, while proton transfer can explain the potentials ofthe CV waves in the presence of added pyridine, simulations of the voltammetry show that proton transferby itself cannot explain the observed reversibility of the second oxidation wave in the presence ofincreasing amounts of added pyridine. This is where H-bonding can play a role. By including H-bondingsteps, and allowing electron transfer and proton transfer to occur through the H-bond complex formedbetween H 2 PD + /pyr and HPD + /Hpyr + , the simulations nicely explain both the observed potential shifts andthe reversibility of the waves. The next question is whether the electron and proton transfer within the H-bonding complex is concertedor step wise. To test this, CV’s were run with 10:1 cyanopyridine:H2PD in 2% D 4 -methanol/acetonitrile or2% H 4 -methanol/acetonitrile. If the second oxidation involved concerted electron-proton transfer, asignificant deuterium isotope effect would be expected, causing a larger ΔE p in the deuterated solventresulting from slower electron transfer. However, no significant difference was observed. Therefore,there is no evidence that the electron-proton transfer is concerted. This result does not by any meansrule out the hypothesis that the proton-electron transfer is occurring within the H-bond complex, it merelyindicates that it is likely that the proton and electron transfer occur in a step-wise fashion within the H-bond complex, and that facilitation of proton-electron transfer by H-bonding can happen even if theprocess is not concerted.

Continuous two-step catalytic conversion of glycerol to pyridine bases in high yield

Glycerol was converted to pyridine bases through a continuous two-step process in a series-connected two-stage fixed-fed reactor. Firstly, dehydration of glycerol to acrolein was achieved in high selectivity over a catalyst FeP-P in the first reactor. The dehydration products were directly introduced into the second reactor charged with a bimetallic catalyst Cu4.6Pr0.3/HZSM-5, contacting ammonia over the catalyst to afford pyridine bases in high yield. Under optimized reaction conditions, the conversion of glycerol was 100%, and the total yield of pyridine base reached up to 60.2%. The catalyst characterization results revealed that the doping of copper and praseodymium did not destroy the frame work of HZSM-5, but increased the Lewis acidity of the catalyst which enhanced the activity and selectivity of the catalyst in the conversion of acrolein to pyridine bases. The doping of minute amount of praseodymium led to the high dispersion of the CuO nanoparticles, thus enhanced the dehydrogenation activity of CuO species, and finally improved the performance of the bimetallic catalyst. In addition, the interaction of copper and praseodymium in the bimetallic catalyst might have positive effect on the performance of the catalyst in the conversion of acrolein to pyridine bases.

Highly Efficient Catalytic Cyclic Carbonate Formation by Pyridyl Salicylimines.

Cyclic carbonates as industrial commodities offer a viable nonredox carbon dioxide fixation, and suitable heterogeneous catalysts are vital for their widespread implementation. Here, we report a highly efficient heterogeneous catalyst for CO2 addition to epoxides based on a newly identified active catalytic pocket consisting of pyridine, imine, and phenol moieties. The polymeric, metal-free catalyst derived from this active site converts less-reactive styrene oxide under atmospheric pressure in quantitative yield and selectivity to the corresponding carbonate. The catalyst does not need additives, solvents, metals, or co-catalysts, can be reused at least 10 cycles without the loss of activity, and scaled up easily to a kilogram scale. Density functional theory calculations reveal that the nucleophilicity of pyridine base gets stronger due to the conjugated imines and H-bonding from phenol accelerates the reaction forward by stabilizing the intermediate.

Alternative bases to 4-tert-butylpyridine for dye-sensitized solar cells employing copper redox mediator

Novel facile synthetic protocol is developed to prepare electrochemically and optically clean Cu(tmby)2TFSI and Cu(tmby)2TFSI2 in a mixture (tmby = 4,4,6,6-tetramethyl-2,2-bipyridine; TFSI = trifluoromethylsufonylimide). This pure Cu(II/I) redox mediator exhibits improved charge-transfer rate at the counterelectrode (PEDOT) and faster diffusion transport in the solution. Four pyridine derivatives: 4-tert-butylpyridine, 2,6-bis-tert-butylpyridine, 4-methoxypyridine and 4-(5-nonyl)pyridine are evaluated as electrolyte additives. Base-specific electrochemical properties of the redox mediator are found for Cu(tmby)22+/+, but not for Co(bpy)33+/2+ which is used as control system. Due to steric hindrance, 2,6-bis-tert-butylpyridine has the smallest influence on the mediator's electrochemistry, but is also ineffective for the VOC enhancement through TiO2 conduction band upshift. Charge-transfer rates at PEDOT surface and diffusion resistances correlate with the basicity (pKa) of the used pyridine derivatives. The dye (Y123)-sensitized solar cells are evaluated by solar conversion performance in addition to electron lifetime, charge extraction and long-term stability tests. The optimization of pyridine bases for the Cu-mediated solar cells represents interplay of basicity and coordination ability. In turn, this allows for tuning of the charge transfer rate at counterelectrode and the mass transport in the electrolyte solution. The 4-(5-nonyl)pyridine is outperforming all the remaining bases in performance metrics of the corresponding solar cells.

Enhanced gas separation performance of an ultramicroporous pillared-layer framework induced by hanging bare Lewis basic pyridine groups.

Pillared-layer metal-organic frameworks show great promise for gas storage and separation because their pore size as well as functionality usually can be controlled and adjusted synergistically. By combining the common pyridine and carboxylate groups, we design herein a new 3D pillared-layer framework, [Co2(DBPT)(BPY)2(CO3)]n (SNNU-95). Dinuclear [Co2] motifs are connected by DBPT ligands to form a 2D layer, which is further bridged by BPY to obtain the 3D pillar-layered framework of SNNU-95. Remarkably, two un-coordinated pyridine groups of DBPT not only help stabilize the 2D layer through ππ stacking but also point into the 1D channels to create an ultramicroporous environment. Taking advantage of the ultramicroporosity and pyridine Lewis basic sites, SNNU-95 shows not only extra high CO2 over CH4 and C2 hydrocarbons over CH4 selectivity, but also remarkable C2H2/CO2, C2H2/C2H4, and C2H4/CO2 separation under ambient conditions. This synergistic effect resulting from functional groups and pore size provides a promising route to design porous materials for the highest possible gas uptake and separation performance.

Influence of Proton Acceptors on the Proton-Coupled Electron Transfer Reaction Kinetics of a Ruthenium-Tyrosine Complex.

A polypyridyl ruthenium complex with fluorinated bipyridine ligands and a covalently bound tyrosine moiety was synthesized, and its photo-induced proton-coupled electron transfer (PCET) reactivity in acetonitrile was investigated with transient absorption spectroscopy. Using flash-quench methodology with methyl viologen as an oxidative quencher, a Ru3+ species is generated that is capable of initiating the intramolecular PCET oxidation of the tyrosine moiety. Using a series of substituted pyridine bases, the reaction kinetics were found to vary as a function of proton acceptor concentration and identity, with no significant H/D kinetic isotope effect. Through analysis of the kinetics traces and comparison to a control complex without the tyrosine moiety, PCET reactivity was found to proceed through an equilibrium electron transfer followed by proton transfer (ET-PT) pathway in which irreversible deprotonation of the tyrosine radical cation shifts the ET equilibrium, conferring a base dependence on the reaction. Comprehensive kinetics modeling allowed for deconvolution of complex kinetics and determination of rate constants for each elementary step. Across the five pyridine bases explored, spanning a range of 4.2 pKa units, a linear free-energy relationship was found for the proton transfer rate constant with a slope of 0.32. These findings highlight the influence that proton transfer driving force exerts on PCET reaction kinetics.

Aromatic versus Aliphatic Carboxyl Group as a Hydrogen Bond Donor in Salts and Cocrystals of an Asymmetric Diacid and Pyridine Derivatives

A series of 15 salts and cocrystals of an asymmetric aromatic–aliphatic dicarboxylic diacid, N-(2-carboxyphenyl)glycine, and pyridine derivatives was synthesized in order to study whether there is a preference of pyridine binding to either of the carboxylic groups. In nine structures the pyridine was bonded to the aliphatic group, in three to both carboxylic groups, and in three to the aromatic group alone. The preference of pyridine derivatives to bond to the aliphatic group correlates with the more positive electrostatic potential on the aliphatic carboxyl hydrogen atom. The occurrence of proton transfer within the structures was found to follow the basicity of the pyridine derivative, four of the least basic pyridines forming cocrystals, two intermediate bases solids with proton disorder and the more basic pyridine derivatives salts. Proton transfer had a considerable effect on the crystal packing, cocrystals mostly comprising discrete molecular complexes, and salt chains of monoanions.

Comparison of classic and microwave-assisted synthesis of benzo-thio crown ethers, and investigation of their ion pair extractions

Macrocyclic benzo-thio crown ethers and benzo-oxo crown ethers were prepared using an esterification–ring closing method. These compounds were synthesised using 2,2′-dithiodibenzoyl chloride, and various glycols and dithiols, in the presence of pyridine base under a nitrogen atmosphere in chloroform. All reactions were performed under reflux condition with conventional heating and microwave (MW) irradiation. The synthesised macrocycles were characterised by FT-IR, 1H NMR, 13C NMR, LC-MS, and elemental analysis methods. Extraction studies have been performed on these original macrocycles using liquid-liquid ion-pair extraction with Li+, Na+, K+, Ni2+, Ca2+, Mg2+, Zn2+, Fe2+,Fe3+, Co3+, Pb2+, Cr3+, Ag+, and Cd2+.The KD, ext.%, ΔG and log KExt values were also calculated. While (U1-U7) ligands exhibits selectivity for Zn2+, Ag+, Ca2+, Pb2+, Fe3+, Cr3+, Co2+, Mg2+, Cd2+, and Ni2+ metal salts, they showed no selectivity for Li+, K+ and Na+ metal salts. Furthermore, Fe3+is the most selective cation for all ligands for competitive extraction. We also observed that microwave heating can have certain benefits over conventional ovens: reaction rate acceleration, milder reaction conditions, higher chemical yield, and lower energy usage. These ligands could be used as metal sensors, enzyme inhibitors, antimicrobial/antifungal agents, and in biological applications.

Separating Proton and Electron Transfer Effects in Three-Component Concerted Proton-Coupled Electron Transfer Reactions.

Multiple-site concerted proton-electron transfer (MS-CPET) reactions were studied in a three-component system. 1-Hydroxy-2,2,6,6-tetramethylpiperidine (TEMPOH) was oxidized to the stable radical TEMPO by electron transfer to ferrocenium oxidants coupled to proton transfer to various pyridine bases. These MS-CPET reactions contrast with the usual reactivity of TEMPOH by hydrogen atom transfer (HAT) to a single e-/H+ acceptor. The three-component reactions proceed by pre-equilibrium formation of a hydrogen-bonded adduct between TEMPOH and the pyridine base, and the adduct is then oxidized by the ferrocenium in a bimolecular MS-CPET step. The second-order rate constants, measured using stopped-flow kinetic techniques, spanned 4 orders of magnitude. An advantage of this system is that the MS-CPET driving force could be independently varied by changing either the pKa of the base or the reduction potential (E°) of the oxidant. Changes in ΔG°MS-CPET from either source had the same effect on the MS-CPET rate constants, and a combined Brønsted plot of ln(kMS-CPET) vs ln(Keq) was linear with a slope of 0.46. These results imply a synchronous concerted mechanism, in which the proton and electron transfer components of the CPET process make equal contributions to the rate constants. The only outliers to the Brønsted correlation are the reactions with sterically hindered pyridines, which apparently hinder the close approach of proton donor and acceptor that facilitates MS-CPET. These three-component reactions are compared with a related HAT reaction of TEMPOH, with the 2,4,6-tri-tert-butylphenoxyl radical. The MS-CPET and HAT oxidations of TEMPOH at the same driving force occurred with similar rate constants. While this is an imperfect comparison, the data suggest that the separation of the proton and electron to different reagents does not significantly inhibit the proton-coupled electron transfer process.

About the Routes of Oxidative Conversion of 2-methyl-5-ethylpyridine on Vanadium Oxide Modified Catalyst

<p>The vapor phase oxidation of 2-methyl-5-ethylpyridine (MEP) on modified vanadium oxide catalyst has been investigated. Di(5-ethyl)-2-pyridil, 2-methyl-5-acethylpyridine and 3-acethylpyridine have been identified as intermediates of MEP oxidation by NMR <sup>13</sup>C spectroscopic and gas chromatography mass spectrometry methods. It has been shown that the interaction between the pyridine base and acidic proton donating sites on the catalyst surface causes an increase of substituents reactivity in 2-position in all stages of 2-methyl-5-ethylpyridine transformation inducing their oxidative elimination. A distinction in composition of the oxidation products is an outcome of a change of the dialkylpyridine substituents in 2- and 5-position contribution. Using literature and experimental data the basic routes of the 2-methyl-5-ethylpyridine oxidative conversion have been determined. The ammoxidation is a process based on the joint oxidation of the initial organic substance and ammonia by air oxygen in the presence of a catalyst [1]. The basic step of ammoxidation is a vapor phase catalytic oxidation, which determines the main routes of the former. Therefore, the obtained results give a possibility for the first time to explain the reason for the change of selectivities during MEP ammoxidation in the present of water.</p>

Fertilizer nitrogen, soil chemical properties, and their determinacy on rice yield: Evidence from 92 paddy fields of a large-scale farm in the Kanto Region of Japan

Rice, a staple crop in Japan, is at risk of decreasing production and its yield highly depends on soil fertility. This study aimed to investigate determinants of rice yield, from the perspectives of fertilizer nitrogen and soil chemical properties. The data were sampled in 2014 and 2015 from 92 peat soil paddy fields on a large-scale farm located in the Kanto Region of Japan. The rice variety used was the most widely planted Koshihikari in Japan. Regression analysis indicated that fertilizer nitrogen significantly affected the yield, with a significant sustained effect to the subsequent year. Twelve soil chemical properties, including pH, cation exchange capacity, content of pyridine base elements, phosphoric acid, and silicic acid, were estimated. In addition to silicic acid, magnesia, in forms of its exchangeable content, saturation, and ratios to potassium and lime, positively affected the yield, while phosphoric acid negatively affected the yield. We assessed the soil chemical properties by soil quality index and principal component analysis. Positive effects were identified for both approaches, with the former performing better in explaining the rice yield. For soil quality index, the individual standardized soil properties and margins for improvement were indicated for each paddy field. Finally, multivariate regression on the principal components identified the most significant properties.

Regioselective Synthesis of 3-Aminoimidazo[1,2-a]pyrimidines with Triflic Anhydride

The regioselective synthesis of 3-aminoimidazo[1,2-a]pyrimidines via triflic anhydride mediated amide activation and intramolecular cyclisation is reported. The nature of the added pyridine base allows access to both regioisomers from a simple common precursor. The method tolerates a range of functional groups and provides access to novel heterocyclic scaffolds.

An All-Organic Proton Battery

Rechargeable batteries that use organic matter as the capacity-carrying material have previously been considered a technology for the future. Earlier batteries in which both the anode and cathode consisted of organic material required significant amounts of conductive additives and were often based on metal-ion electrolytes containing Li+ or Na+. However, we have used conducting poly(3,4-ethylenedioxythiophene) (PEDOT), functionalized with anthraquinone (PEDOT-AQ) or benzonquinone (PEDOT-BQ) pendant groups as the negative and positive electrode materials, respectively, to make an all-organic proton battery devoid of metals. The electrolyte consists of a proton donor and acceptor slurry containing substituted pyridinium triflates and the corresponding pyridine base. This slurry allows the 2e-/2H+ quinone/hydroquinone redox reactions while suppressing proton reduction in the battery cell. By using strong (acidic) proton donors, the formal potential of the quinone redox reactions is tuned into the potential region in which the PEDOT backbone is conductive, thus eliminating the need for conducting additives. In this all-organic proton battery cell, PEDOT-AQ and PEDOT-BQ deliver 103 and 120 mAh g-1, which correspond to 78% and 75%, respectively, of the theoretical specific capacity of the materials at an average cell potential of 0.5 V. We show that PEDOT-BQ determines the cycling stability of the device while PEDOT-AQ provides excellent reversibility for at least 1000 cycles. This proof-of-concept shows the feasibility of assembling all-organic proton batteries which require no conductive additives and also reveals where the challenges and opportunities lie on the path to producing plastic batteries.

Functional solid additive modified PEDOT:PSS as an anode buffer layer for enhanced photovoltaic performance and stability in polymer solar cells

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is most commonly used as an anode buffer layer in bulk-heterojunction (BHJ) polymer solar cells (PSCs). However, its hygroscopic and acidic nature contributes to the insufficient electrical conductivity, air stability and restricted photovoltaic (PV) performance for the fabricated PSCs. In this study, a new multifunctional additive, 2,3-dihydroxypyridine (DOH), has been used in the PEDOT: PSS buffer layer to obtain modified properties for PEDOT: PSS@DOH and achieve high PV performances. The electrical conductivity of PEDOT:PSS@DOH films was markedly improved compared with that of PEDOT:PSS. The PEDOT:PSS@DOH film exhibited excellent optical characteristics, appropriate work function alignment, and good surface properties in BHJ-PSCs. When a poly(3-hexylthiohpene):[6,6]-phenyl C61-butyric acid methyl ester blend system was applied as the photoactive layer, the power conversion efficiency of the resulting PSCs with PEDOT:PSS@DOH(1.0%) reached 3.49%, outperforming pristine PEDOT:PSS, exhibiting a power conversion enhancement of 20%. The device fabricated using PEDOT:PSS@DOH (1.0 wt%) also exhibited improved thermal and air stability. Our results also confirm that DOH, a basic pyridine derivative, facilitates adequate hydrogen bonding interactions with the sulfonic acid groups of PSS, induces the conformational transformation of PEDOT chains and contributes to the phase separation between PEDOT and PSS chains.

Mitigation strategy towards stabilizing the Electrochemical Interface under high CO and H2O containing reformate gas feed

Despite the enhanced CO tolerance of the high temperature polymer electrolyte membrane (HT PEMFC) technology, the synergistic effect of CO and steam in the anodic reformate gas feed was proven to result in serious performance reduction and operation instabilities, due to the dynamic disturbance of the electrochemical interface (EI). In this work a mitigation strategy is presented by controlling the hydrophilicity of the catalytic layer in order to achieve the optimum structure of the EI. The thin and continuous film distribution of the phosphoric acid (PA) inside the catalytic layer (CL) without blocking the pores is the main characteristic property that determines the good quality of the EI. As shown, a hydrophilic catalytic layer is preferable, since the acid, being at any hydration level, will be able to spread over the catalytic surface aiming to the formation of a thin and continuous film so as to maximize the extend of the EI without blocking the pores of the catalytic layer. This facilitates the uninterrupted transport of protons and the fast diffusion of the reacting gases. Herein, this was accomplished by modifying the surface properties of the CL through the anchoring of pyridine moieties on the MWCNTs, which plays the role of the Pt catalyst support. The basic pyridine moieties enhance the hydrophilicity of the nanotubes through the acid (PA)-base (pyridine) interaction so that the contact angle between a PA drop and the catalytic layer is very close to zero. The good affinity of the PA with the pyridine based catalytic layer secures the PA thin film distribution and continuity. More importantly it is not affected even at high hydration levels of the PA, when the partial pressure of steam is increased at values>20kPa. Otherwise, on conventional C supports, hydrated PA has the tendency to shrink and create ganglia leading to the disruption of the EI. The pyridine modified catalytic layers approach Pt surface utilization values as high as 80% as compared to 50% utilization measured for the case of conventional Pt/C catalytic layers.

Effect of Si/Al Ratios on the Structure and Catalytic Properties of Alkaline-Treated ZSM-5 Catalysts

A series of hierarchical HZSM-5 catalysts were synthesized by alkaline (denoted as HZSM-5-At) and/or alkaline-acid (denoted as HZSM-5-At-acid) treatments, and they as catalyst pairs were employed for the synthesis of glycerol and ammonia toward pyridine bases in a series-connected two-stage reactor. The characterization was analysed by means of N2-physorption and NH3-TPD techniques. The catalytic evaluation showed that the lower Si/Al ratio (Si/Al = 25 before treatment) in catalyst pairs (HZSM-5-At + ZnO/HZSM-5-At-acid) possessed the highest total yield of pyridine bases among all the catalyst pairs, but the suitable Si/Al ratio in alkaline-treated ZSM-5 (Si/Al = 38 before treatment) in the first stage of reactor and ZnO/HZSM-5-At-acid (Si/Al = 25 before treatment) in the second stage of reactor had the stronger stability relative to other catalyst pairs. The characterization revealed that the amount of acid sites play a vital role in the formation of pyridine bases whereas the appearance of mesoporous structure and the declined concentration of acid sites were main reasons for promoting the stability.

Enhanced selectivity in the conversion of glycerol to pyridine bases over HZSM-5/11 intergrowth zeolite

Intergrown zeolite HZSM-5/11(78) catalyst showed enhancement in the conversion of glycerol with ammonia to pyridine bases.

Ozonolysis of isoquinoline in a polystyrene-based sulfonate cation exchanger

Nanoreactor ozonolysis of aromatic heterocycles is studied. It is found that cinchomeronic acid (which is used in the production of medical preparations) may be obtained by the nanoreactor ozonolysis of isoquinoline, which is a component of the heavy pyridine bases obtained in the distillation of coal tar.