Backward Reaction Research Articles

Self-Consistency of the Theory of Elementary Stage Rates of Reversible Processes and the Equilibrium Distribution of Reaction Mixture Components

An analysis is presented of one of the key concepts of physical chemistry of condensed phases: the theory self-consistency in describing the rates of elementary stages of reversible processes and the equilibrium distribution of components in a reaction mixture. It posits that by equating the rates of forward and backward reactions, we must obtain the same equation for the equilibrium distribution of reaction mixture components, which follows directly from deducing the equation in equilibrium theory. Ideal reaction systems always have this property, since the theory is of a one-particle character. Problems arise in considering interparticle interactions responsible for the nonideal behavior of real systems. The Eyring and Temkin approaches to describing nonideal reaction systems are compared. Conditions for the self-consistency of the theory for mono- and bimolecular processes in different types of interparticle potentials, the degree of deviation from the equilibrium state, allowing for the internal motions of molecules in condensed phases, and the electronic polarization of the reagent environment are considered within the lattice gas model. The inapplicability of the concept of an activated complex coefficient for reaching self-consistency is demonstrated. It is also shown that one-particle approximations for considering intermolecular interactions do not provide a theory of self-consistency for condensed phases. We must at a minimum consider short-range order correlations.

A Numerical Investigation on NO2 Formation in a Natural Gas–Diesel Dual Fuel Engine

This research numerically simulates the formation and destruction of nitrogen dioxide (NO2) in a natural gas (NG)–diesel dual fuel engine using commercial CFD software converge coupled with a reduced primary reference fuel (PRF) mechanism consisting of 45 species and 142 reactions. The model was validated by comparing the simulated cylinder pressure, heat release rate (HRR), and nitrogen oxide (NOx) emissions with experimental data. The validated model was used to simulate the formation and destruction of NO2 in a NG–diesel dual fuel engine. The formation of NO2 and its correlation with the local concentration of nitric oxide (NO), methane, and temperature were examined and discussed. It was revealed that NO2 was mainly formed in the interface region between the hot NO-containing combustion products and the relatively cool unburnt methane–air mixture. The NO2 formed at the early combustion stage is usually destructed to NO after the complete oxidation of methane and n-heptane, while NO2 formed during the postcombustion process survives through the expansion process and exits the engine. The increased NO2 emissions from NG–diesel dual fuel engines was formed during the post combustion process due to higher concentration of HO2 produced during the oxidation process of the unburned methane at low temperature. A detailed analysis of the chemical reactions occurring in the NO2 containing zone consisting of NO2, NO, O2, methane, etc., was conducted using a quasi-homogeneous constant volume (QHCV) model to identify the key reactions and species dominating NO2 formation and destruction. The HO2 produced during the postcombustion process of methane was identified as the primary species dominating the formation of NO2 during the post combustion expansion process. The simulation revealed the key reaction path for the formation of HO2 noted as CH4 → CH3 → CH2O → HCO → HO2, with conversion ratios of 98%, 74%, 90%, 98%, accordingly. The backward reaction of OH + NO2 = NO + HO2 consumed 34% of HO2 for the production of NO2.

Experimental and kinetic studies of the effect of CO2 dilution on laminar premixed n-heptane/air flames

In the present study, experimental and kinetic studies of the effect of CO2 dilution on laminar premixed n-heptane/air flames were performed via the outwardly propagating spherical flames and the simulation of one-dimensional planar flames. The laminar flame speeds and Markstein lengths of n-heptane/air/CO2 mixtures at different CO2 dilution rates were measured and the chemical effect of CO2 was separated from its total effects by introducing a type of fictitious carbon dioxide (FCO2) in the simulation. Results show that the laminar flame speeds of n-heptane/air/CO2 mixtures nonlinearly decrease with the increase of CO2 dilution rate. Moreover, as CO2 dilution rate increases, the instability of laminar n-heptane/air/CO2 flames decreases due to the decrease of the hydro-dynamic instability. The results of kinetic analysis show the increase of CO2 concentration in the n-heptane/air flames decreases the peaks of mole fractions of the main radical species (OH, O, H, CH3 and HO2), net reaction rates of the main elementary reactions and flame temperature. Both the physical and chemical effects of CO2 suppress the laminar flame speeds and flame temperatures and inhibit the productions of the main radical species and net reaction rates of the main elementary reactions, and the former dominates. The chemical effect of CO2 remarkably promotes the production of CO via shifting the equilibrium of R24 CO + OH = CO2 + H, and the third-body effect of CO2 slightly increases the production of H2O shifting the equilibrium of R8 H2O + M = H + OH + M. The backward reactions of R24 and R8 enhanced by CO2 addition compete with the important chain branching reaction R1 H + O2 = O + OH for H atoms, which plays the chemical role in reducing the laminar flame speed and flame temperature.

An Unprecedented Retro-Mumm Rearrangement Revealed by ESI-MS/MS, IRMPD Spectroscopy, and DFT Calculations.

Brønsted acids and protic solvents mediate acyl transfer, known as the Mumm rearrangement, from imidates to the corresponding acylamides. This represents a key step in several reactions, for example, the Ugi four-component reaction (U-4CR) and Passerini three-component reaction (P-3CR). Herein, an unprecedented break of the non-reversibility of the Mumm rearrangement is reported. A combination of electrospray tandem mass spectrometry (ESI-MS/MS), infrared multiphoton dissociation (IRMPD) ion spectroscopy and theoretical calculations demonstrates the occurrence of the retro-Mumm rearrangement of protonated isopeptides in the gas phase. In the gas phase, the extra proton acquired during ESI promotes the backward isomerisation reaction in a catalytic fashion.

An innovative approach for storing low-grade thermal energy using liquid phase thermoreversible reaction

This study investigates the potential of “methanol+acetaldehyde↔hemiacetal” as a liquid phase thermoreversible reaction for long-term storing of low-grade thermal energy to overcome the mismatch between energy supply and demand. Both forward and backward reactions are studied experimentally and the technical issues associated with employing such a system are discussed. Methanol and acetaldehyde would react via an exothermic reaction (-ΔHr=31.8kJmoleor104.7kWhm3) at low temperature range (<15 °C) and atmospheric pressure, with a high reaction rate (k=26.26×102exp-4099T). The regeneration of parent reactants with high purity occurs at 48 °C which can easily be delivered using low-grade heat. The low operating temperature required for forward reaction and the reduction in backward reaction rate caused by methanol accumulated are the main engineering challenges. These technical problems need to be solved before this reaction could be utilised commercially.

Kinetics and Mechanism of Oxirane Formation by Darzens Condensation of Ketones: Quantification of the Electrophilicities of Ketones

The kinetics of epoxide formation by Darzens condensation of aliphatic ketones 1 with arylsulfonyl-substituted chloromethyl anions 2 (ArSO2CHCl-) have been determined photometrically in DMSO solution at 20 °C. The reactions proceed via nucleophilic attack of the carbanions at the carbonyl group to give intermediate halohydrin anions 4, which subsequently cyclize with formation of the oxiranes 3. Protonation of the reaction mixture obtained in THF solution at low temperature allowed the intermediates to be trapped and the corresponding halohydrins 4-H to be isolated. Crossover experiments, i.e., deprotonation of the halohydrins 4-H in the presence of a trapping reagent for the regenerated arylsulfonyl-substituted chloromethyl anions 2, provided the relative rates of backward ( k-CC) and ring closure ( krc) reactions of the intermediates. Combination of the kinetic data ( k2exptl) with the splitting ratio ( k-CC/ krc) gave the second-order rate constants kCC for the attack of the carbanions 2 at the ketones 1. These kCC values and the previously reported reactivity parameters N and sN for the arylsulfonyl-substituted chloromethyl anions 2 allowed us to use the linear free energy relationship log k2(20 °C) = sN( N + E) for deriving the electrophilicity parameters E of the ketones 1 and thus predict potential nucleophilic reaction partners. Density functional theory calculations of the intrinsic reaction pathways showed that the reactions of the ketones 1 with the chloromethyl anions 2 yield two rotational isomers of the intermediate halohydrin anions 4, only one of which can cyclize while the other undergoes retroaddition because the barrier for rotation is higher than that for reversal to the reactants 1 and 2. The electrophilicity parameters E correlate moderately with the lowest unoccupied molecular orbital energies of the carbonyl groups, very poorly with Parr's electrophilicity indices, and best with the methyl anion affinities calculated for DMSO solution.

A Neutral RuII Hydride Complex for the Regio- and Chemoselective Reduction of N-Silylpyridinium Ions.

A detailed experimental analysis of the 1,4-selective reduction of pyridine with hydrosilanes catalyzed by a coordinatively unsaturated RuII thiolate complex is reported. The previously suggested intermediates, N-silylpyridinium ions and a neutral RuII hydride, have been independently synthesized and do indeed participate in the catalytic cycle. The resting state is not the cationic RuII complex initially used as the catalyst but its pyridine-coordinated congener. All RuII complexes, including the one resulting from hydrosilane activation, are in equilibrium with each other. The N-silylated 1,4-dihydropyridine together with the cationic RuII complex convert back into the corresponding N-silylpyridinium ion and the neutral RuII hydride (retro-hydrosilylation), followed by further backward reaction into the hydrosilane and the pyridine adduct of the cationic complex. These steps prove the overall reversibility of the transformation.

APPLICATION OF THERMODYNAMIC MODELLING AND EXPERIMENTAL INVESTIGATION OF LEACHING YTTRIUM FROM LIQUID CRYSTAL DISPLAY

Thermodynamic modelling, experiment, measurement, and characterization technique were used to evaluate the leaching process of yttrium (Y) elements from liquid crystal display (LCD) electronic waste (e-waste). Thermodynamic modelling using HSC 6.0 software revealed that the reaction of leaching out Y with hydrochloric acid is endothermic thus absorbing heat and at the same time positive Gibbs free energy from temperature 273.15 K to 343.15 K and negative Gibbs free energy from temperature 353.15 K to 373.15 K. Thermodynamic data of the leaching processes with sulfuric and nitric acids show that the reactions are exothermic thus release heat and at the same time negative Gibbs free energy from temperature 273.15K and above. The leaching reaction with sulfuric and nitric acids identified to be reversible from temperature 273.15 K and above due to the negative entropy change, whereas the reaction was found irreversible for the hydrochloric acid solution due to the positive entropy change at the similar minimum temperature setting. The significance of reversibility versus irreversibility is their relationship to the efficiency. The equilibrium constant show that the leaching process with hydrochloric acid is less than 1 (Log K&lt;1) from temperature 273.15 K to 343.15 K indicate that the backward reaction is favored while from temperature 353.15 K to 373.15 K have a positive equilibrium constant (Log K&gt;1) thus indicate thatforward reaction is favored. Leaching process with sulfuric and nitric acids shows that the positive equilibrium constant (Log K&gt;1) which indicate that forward reaction is favored from temperature 273.15 K and above. The Pourbaix diagram modelling showed that Y dissolved in HCl at pH below 7 therefore strong reducing agents such as sulfuric acid (sulfide) can improve the dissolution of Y. Inductively coupled plasma mass spectroscopy (ICP-MS) results showed that only Y is viable to be efficiently leached from the studied LCD, e-waste either in a single-stage or in two-stage leachingmode. Sulfuric and nitric acids are found to be the most practical solutions in leaching out the Y element whereby around 0.00515 ppm and 0.00507 ppm of Y were dissolved in both solutions respectively based on the two-stages leaching approach.

Interconnected ZrO2 doped ZnO/TiO2 network photoanode for dye-sensitized solar cells

In this study, ZrO2 surface modified ZnO/TiO2 composite film is adapted as photoanode in dye sensitized solar cells (DSSCs) and compared with un-passivated ZnO/TiO2 DSSC performance. The performance is investigated by dark and photocurrent density–voltage ( J–V) characteristics, quantum efficiency and electrochemical impedance spectroscopy. The J–V characteristics shows that DSSCs with ZrO2 surface passivation produces significantly high open-circuit voltage of 0.87 V, short-circuit current density of 13.6 mA cm−2, fill factor of 0.65 and a power conversion efficiency of ∼6.97% under simulated AM1.5 solar irradiation. The higher onset potential in the dark, larger open-circuit potential under illumination, and an enhancement in power conversion efficiency strongly suggests an efficient suppression of back electron transfer from the conduction band of the hetero-phase junctions to the oxidized species in the electrolyte as established by dark and illuminated J–V characteristics. Thus, the oxidized dye molecules are readily regenerated by a redox couple dissolved in an electrolyte, allowing more photon excitation by dye molecules. The electrochemical impedance data extracts further provide additional evidence of the enhancement in photocurrent and lower charge carrier resistances observed in ZrO2/ZnO/TiO2/dye photoelectrode. With the ZrO2 surface modification, main loss mechanism in the device is suppressed and backward recombination reaction is minimized.

Z-schematic water splitting by the synergistic effect of a type-II heterostructure and a highly efficient oxygen evolution catalyst

Artificial Z-scheme system inspired by the natural photosynthesis in green plants has attracted extensive attention owing to its advantages such as simultaneously wide range light absorption, highly efficient charge separation and strong redox ability. In this paper, we report the synthesis of a novel all-solid-state direct Z-scheme photocatalyst of Ag3PO4/CeO2/TiO2 by depositing Ag3PO4 nanoparticles (NPs) on CeO2/TiO2 hierarchical branched nanowires (BNWs), where the CeO2/TiO2 BNWs act as a novel substrate for the well dispersed nano-size Ag3PO4. The Ag3PO4/CeO2/TiO2 photocatalyst exhibits excellent ability of photocatalytic oxygen evolution from pure water splitting. It is suggested that the Z-scheme charge transfer route between CeO2/TiO2 and Ag3PO4 improves the redox ability. On the other hand, the cascade energy level alignment in CeO2/TiO2 BNWs expedites the spatial charge separation, and hence suppresses photocatalytic backward reaction. However, it is difficult to realize a perfect excitation balance in Ag3PO4/CeO2/TiO2 and the composite still surfers photo-corrosion in photocatalysis reaction. Nevertheless, our results provide an innovative strategy of constructing a Z-scheme system from a type-II heterostructure and a highly efficient oxygen evolution catalyst.

Efficient Redox-Mediator-Free Z-Scheme Water Splitting Employing Oxysulfide Photocatalysts under Visible Light

Oxysulfides, which exhibit intense visible light absorption and high photocatalytic activity during hydrogen evolution, are promising photocatalysts for Z-scheme water splitting. However, the realization of efficient Z-scheme water splitting using oxysulfides as hydrogen evolution photocatalysts (HEPs) has been hampered by backward reactions involving reversible redox couples, the low efficiency of interparticle electron transfer, and a lack of knowledge regarding the means of promoting hydrogen evolution activity under nonsacrificial conditions. In this study, La5Ti2CuS5O7 was found to realize water splitting without any redox mediator by constructing Z-scheme-type photocatalyst sheets with BiVO4 as the oxygen evolution photocatalyst. It is also demonstrated that p-type doping and the formation of a La5Ti2Cu0.9Ag0.1S5O7 solid solution effectively enhance the water-splitting activity of the photocatalyst sheet. An apparent quantum yield of 4.9% at 420 nm and a solar to hydrogen energy conversion efficienc...

Process intensification using a spiral capillary microreactor for continuous flow synthesis of performic acid and it’s kinetic study

The continuous production of performic acid is getting significant importance due to it’s versatile oxidizing properties in various applications such as in the food, oil and chemical industries. In this work, an attempt has been made for synthesis of performic acid in a continuous flow microreator in polytetrafluoroethylene spiral capillary microreactor (PSCMR) with and without homogeneous catalyst. The effect of catalyst concentration, hydrogen peroxide concentration, temperature and radius of curvature on formation of perfomic acid was studied. The maximum conversion of FA was obtained within 6 min at 30 °C and 4 mol% catalyst. The maximum PFA was obtained (5.175 mol/L) when the reaction was performed in spiral capillary microreactor having 13.25 mm radius of curvature (Number of turns = 21). However, in the radius of curvature of 18.25 mm (Number of turns = 15) and 23.25 mm (Number of turns = 12) of the PSCMR gave 3.393 mol/L and 3.105 mol/L of PFA respectively at residence time of 9 min. Based on the kinetic equations and experimental data, the kinetic constants were determined. Thus, the average rate constants for forward and backward reaction are 0.0097 and 0.04354 L/(mol min) respectively. Based on the kinetic data, it was found that the activation energies of PFA synthesis and hydrolysis were 31.716 and 13.701 kJ/mol respectively.

Kinetics of nopyl acetate synthesis by homogeneously catalyzed esterification of acetic acid with nopol

The esterification of nopol with acetic acid to produce nopyl acetate using sulfuric acid as homogeneous catalyst was studied. The reactions were carried out in a batch reactor, at different temperatures (50, 60, 70 and 80 °C), catalyst concentrations (0.0184, 0.0275, 0.0367 and 0.0480 mol L -1 ) and molar ratio of acetic acid to nopol (1: 1, 1:2, 1:3 and 1: 4); the chemical equilibrium composition was measured at those reaction conditions. It was found that the equilibrium composition is a weak function of temperature, equilibrium conversion was 63, 68, 71 and 75% at 50, 60, 70 and 80°C, respectively. The reaction was described with a simple power-law model with a second-order kinetic model for both the forward and the backward reaction, using concentration and activities which were predicted by the Universal Functional group Contribution (UNIFAC) method for considering non-ideal behavior of the liquid phase. The forward reaction rate and the equilibrium constants increased with temperature; the relation of the pre-exponential factor with the catalyst amount was evaluated. The activation energy and pre-exponential factor estimated for the forward reaction using the kinetic model based on concentration, were respectively, 28.08 kJ mol -1 and 11126 L mol -1 h -1 with a concentration of catalyst of 0.0275 M. Using the kinetic model based on activities, the forward reaction rate constant was 28.56 kJ·mol -1 and the k fo,act was 33860 L mol -1 h -1 . The enthalpy (34.90 kJ mol -1 ) and the entropy (0.12 kJ mol -1 K -1 ) of reaction were determined using van’t Hoff equation.

Modification of Ga2O3 by an Ag-Cr core-shell cocatalyst enhances photocatalytic CO evolution for the conversion of CO2 by H2O.

A core-shell structure of Ag-Cr dual cocatalyst loaded-Ga2O3 was found to significantly enhance the formation rate of CO and selectivity toward CO evolution for the photocatalytic conversion of CO2 where H2O is used as an electron donor.

Determination of Equilibrium Constant and Relative Brightness in FRET-FCS by Including the Third-Order Correlations.

Fluorescence correlation spectroscopy (FCS) encodes the information on the equilibrium constant (K), the relative fluorescence brightness of fluorophore (Q), and the forward and backward reaction rate constants (k+ and k-) on a physical or chemical relaxation. However, it has been a long-standing problem to completely resolve the FCS data to get the thermodynamic and kinetic information. Recently, we have solved the problem for fluorescence autocorrelation spectroscopy (FACS). Here, we extend the method to fluorescence cross-correlation spectroscopy (FCCS), which appears when FCS is coupled with fluorescence resonance energy transfer (FRET). Among 12 total second-order and third-order pre-exponential factors in a relaxation process probed by the FRET-FCS technique, 3 are independent. We presented and discussed 3 sets of explicit solutions to use these pre-exponential factors to calculate K and Q. Together with the relaxation time, the acquired K will allow people to obtain k+ and k-, so that the goal of deciphering the FRET-FCS data will be fully reached. The theory is verified by extensive computer simulations and tested experimentally on a system of oligonucleotide hybridization.

Production of eco-friendly poly(oxymethylene) dimethyl ethers catalyzed by acidic ionic liquid: A kinetic investigation

Large scale green production of poly(oxymethylene) dimethyl ethers(DMMn) would be crucial if the diesel-DMMn blends were applied to tackle the worldwide formidable air pollution by particulate matter. Kinetics studies are of great significance among the core challenges for understanding the reaction principles and process design. Kinetic model was developed for the production of DMMn from methylal and trioxane with sulfonic acid-functionalized ionic liquid as catalyst. Reversible reactions of propagation-depolymerization were simultaneously considered with non-equal rate constants for complex sequential reactions. The kinetic model proposed showed good accuracy and consistency for both forward and backward reactions. Activation energies Ep were in the range of 35.7 to 39.6 kJ mol−1 for DMMn propagation reactions and 50.8 to 54.7 kJ mol−1 for DMMn decomposition, with the difference of −15.1 kJ mol−1 determined by Arrhenius equation. Entropy of activation, determined by Eyring-Polanyi equation, could make a significant contribution to the Gibbs energy barrier in the DMMn propagation/decomposition. It is interesting that the Schulz-Flory type distribution still could be maintained even the calculated rate constants increased with DMMn chain length.

Kinetic modeling studies of SOA formation from &amp;lt;i&amp;gt;α&amp;lt;/i&amp;gt;-pinene ozonolysis

Abstract. This paper describes the implementation of a kinetic gas-particle partitioning approach used for the simulation of secondary organic aerosol (SOA) formation within the SPectral Aerosol Cloud Chemistry Interaction Model (SPACCIM). The kinetic partitioning considers the diffusion of organic compounds into aerosol particles and the subsequent chemical reactions in the particle phase. The basic kinetic partitioning approach is modified by the implementation of chemical backward reaction of the solute within the particle phase as well as a composition-dependent particle-phase bulk diffusion coefficient. The adapted gas-phase chemistry mechanism for α-pinene oxidation has been updated due to the recent findings related to the formation of highly oxidized multifunctional organic compounds (HOMs). Experimental results from a LEAK (Leipziger Aerosolkammer) chamber study for α-pinene ozonolysis were compared with the model results describing this reaction system.The performed model studies reveal that the particle-phase bulk diffusion coefficient and the particle-phase reactivity are key parameters for SOA formation. Using the same particle-phase reactivity for both cases, we find that liquid particles with higher particle-phase bulk diffusion coefficients have 310 times more organic material formed in the particle phase compared to higher viscous semi-solid particles with lower particle-phase bulk diffusion coefficients. The model results demonstrate that, even with a moderate particle-phase reactivity, about 61 % of the modeled organic mass consists of reaction products that are formed in the liquid particles. This finding emphasizes the potential role of SOA processing. Moreover, the initial organic aerosol mass concentration and the particle radius are of minor importance for the process of SOA formation in liquid particles. A sensitivity study shows that a 22-fold increase in particle size merely leads to a SOA increase of less than 10 %.Due to two additional implementations, allowing backward reactions in the particle phase and considering a composition-dependent particle-phase bulk diffusion coefficient, the potential overprediction of the SOA mass with the basic kinetic approach is reduced by about 40 %. HOMs are an important compound group in the early stage of SOA formation because they contribute up to 65 % of the total SOA mass at this stage. HOMs also induce further SOA formation by providing an absorptive medium for SVOCs (semi-volatile organic compounds). This process contributes about 27 % of the total organic mass. The model results are very similar to the LEAK chamber results. Overall, the sensitivity studies demonstrate that the particle reactivity and the particle-phase bulk diffusion require a better characterization in order to improve the current model implementations and to validate the assumptions made from the chamber simulations. The successful implementation and testing of the current kinetic gas-particle partitioning approach in a box model framework will allow further applications in a 3-D model for regional-scale process investigations.

Stress induced by diffusion, curvature, and reversible electrochemical reaction in bilayer lithium-ion battery electrode plates

In this paper, a new reaction-diffusion model, coupling the reversible electrochemical reaction, Lithium (Li) diffusion, and bending, is proposed to investigate the curvature, neutral axis movement, and stress in bilayer electrode. Bending curvature and stress, for the first time, are analytically and numerically investigated relate to both the diffusion and the reversible electrochemical reaction. The results reveal that the reversible electrochemical reaction retards the lithiation process, leading to the slowing down of diffusion process. Two neutral axes exist in the active plate due to a gradient of mechanical properties during lithiation. The reaction makes the stress turn to compressive-state at the side surface of active plate, and more violent reaction aggravates this compressive stress during charging. Moreover, the reaction alleviates the compressive stress at interface, and limits the movement of the maximum tensile stress to the interface or the side surface of the active plate where the manufacturing defects are often present, thus eliminating the surface or interface fracture behaviors. The effect of the backward reaction is found to be ignorable under potentiostatic charging. Finally, the thickness ratio of current collector to active plate should be less than 0.3 on the premise of strength requirement. Current collector should be fabricated as softly as possible to mitigate the adverse stress.

CuO[sbnd]Cr2O3 core-shell structured co-catalysts on TiO2 for efficient photocatalytic water splitting using direct solar light

Synthesis of core-shell structured CuOCr2O3 nanoparticles as co-catalyst to improve the photocatalytic hydrogen evolution performance of TiO2 was demonstrated. The effect of co-catalyst loading on TiO2 and the nature of the reactor was found to be more significant for H2 production under direct solar light. The formation of 9.3 nm Cr2O3 shell over CuO core in the CuOCr2O3 nanostructured co-catalyst was confirmed using transmission electron microscopy. A very high H2 production rate of 82.39 and 70.4 mmol h−1 g−1cat was observed with quartz and pyrex reactors under direct solar light of irradiation 96–100 mW/cm2, respectively. This is almost three times higher than that of bare TiO2 under similar experimental conditions. The core-shell co-catalyst loaded on TiO2 by simple mechanical mixing method which is useful for bulk scale synthesis in practical applications. The observed high H2 production was explained with plausible mechanism where the synergic effect of CuOCr2O3 co-catalyst loaded TiO2 surface that reduces the effective charge carriers recombination and impeded backward reaction by the Cr2O3 thin layer. The presence of Cu2+ and absence of Cu+ and metallic Cu was confirmed using XPS analysis. The effect of co-catalyst loading and sacrificial agent concentration on the photocatalytic hydrogen production was also reported. The stability of the CuOCr2O3 core-shell NPs loaded TiO2 photocatalyst under the direct solar light was examined by continuous cycling for three days and it was found to be 81 and 70% of photocatalyst activity is retained after 3 days in the quartz and pyrex reactor systems, respectively.

Desktop NMR spectroscopy for real-time monitoring of an acetalization reaction in comparison with gas chromatography and NMR at 9.4T.

Monitoring of chemical reactions in real-time is in demand for process control. Different methods such as gas chromatography (GC), mass spectroscopy, infrared spectroscopy, and nuclear magnetic resonance (NMR) are used for that purpose. The current state-of-the-art compact NMR systems provide a useful method to employ with various reaction conditions for studying chemical reactions inside the fume hood at the chemical workplace. In the present study, an acetalization reaction was investigated with compact NMR spectroscopy in real-time. Acetalization is used for multistep synthesis of the variety of organic compounds to protect particular chemical groups. A compact 1T NMR spectrometer with a permanent magnet was employed to monitor the acid catalyzed acetalization of the p-nitrobenzaldehyde with ethylene glycol. The concentrations of both reactant and product were followed by peak integrals in single-scan 1H NMR spectra as a function of time. The reaction conditions were varied in terms of temperature, agitation speed, catalyst loading, and feed concentrations in order to determine the activation energy with the help of a pseudo-homogeneous kinetic model. For low molar ratios of aldehyde and glycol, the equilibrium conversions were lower than for the stoichiometric ratio. Increasing catalyst concentration leads to faster conversion. The data obtained with low-field NMR spectroscopy were compared with data from GC and NMR spectroscopy at 9.4T acquired in batch mode by extracting samples at regular time intervals. The reaction kinetics followed by either method agreed well. The activation energies for forward and backward reactions were determined by real-time monitoring with compact NMR at 1T were 48±5 and 60±4kJ/mol, respectively. The activation energies obtained with gas chromatography for forward and backward reactions were 48±4 and 51±4kJ/mol. The equilibrium constant decreases with increasing temperature as expected for an exothermic reaction. The impact of dense sampling with online NMR and sparse sampling with GC was observed on the kinetic outcome using the same kinetic model. Graphical abstract Acetalization reaction kinetics were monitored with real-time desktop NMR spectroscopy at 1T. Each data point was obtained at regular intervals with a single shot in 15s. The kinetics was compared with sparsely sampled data obtained with GC and NMR at 9.4T.