Search

The Langmuir-Hinshelwood formalism describes catalytic reactions of Langmuirian surface species under the assumption that all adsorbates are randomly-distributed – enabling adjacency of surface-bound intermediates to be determined solely by coverages of single-site occupants. We demonstrate herein that this approximation is inappropriate even for simple catalytic reactions (e.g. A + A → A2) and manifestly neglects islanding of slowly-consumed species and partitioning of highly-reactive species inherently engendered by ≥ two-site elementary steps (e.g. A*–A* → A2(g) + *–*). Rigorous description of kinetically-consequential islanding/partitioning phenomena requires explicit description of the coverage and chemical dynamics of all multi-site ensembles. Higher-order, ensemble-specific rate terms identify the particular microscopic events relevant to each ensemble, and, in doing so, reveal that each elementary step (e.g. A(g) adsorption) describes not one event (e.g. A(g) + * → A*) , but a sum over all ensemble-specific paths (e.g. A(g) + *–* → A*–* and A(g) + A*–* → A*–A*). De-convoluting each elementary step into its constituent multi-site paths proffers kinetic detail otherwise inaccessible – enabling (i) identification of rate- and selectivity-determining site ensembles, (ii) calculation of rates and degrees of rate control of ensemble-specific elementary steps, (iii) incorporation of adsorbate surface diffusion, (iv) incorporation of lateral adsorbate interactions, and (v) quantitative description of catalysis of multi-site-occupying intermediates (e.g. *CnHm* species in hydrocarbon (de-)hydrogenation and C-C bond coupling/cleavage reactions) which we demonstrate is inaccessible to the Langmuir-Hinshelwood formalism even if adsorbate surface diffusion is infinitely-fast.

In heterogeneous catalysis, the LH (Langmuir Hinshelwood) mechanism is more efficient and recommended over any other mechanism adopted for CO oxidation. However, the LH mechanism over a carbon surface is a challenge and is paused to be applied to any carbon surface in practical application. In this work, we carried out density functional theory to study how the incorporation of nitrogen, boron atom (C→N, C→B) and co-doping on graphene nanoribbons can modify the catalytic activity of the surface and the preference between ER (Eley-Ridel) and LH mechanism is explored. Boron plays a crucial role in the adsorption of both CO and O2, whereas nitrogen doping can only activate O2 molecule through altering the triplet ground state. Considering the activation energy for the first CO2 formation and CO binding strength, we have defined a window to identify the operation of the LH mechanism in the catalysis. 3B edge doped AGNR (armchair graphene nanoribbon doped with three boron atoms at its edge) is identified as an active catalyst for the CO oxidation through the LH mechanism, with the SA (Sabatier activity) and TOF (turnover frequency) values of 0.90 and 2.47, respectively. This approach will help to search for metal-free catalysts for the CO oxidation with the efficient LH mechanism.

Synthesis of copper-doped TiO2 (Cu:TiO2) and undoped TiO2 were performed by the sol–gel method. These photocatalysts were characterized by Raman spectroscopy, XRD, and diffuse reflectance. The synthesized catalysts were fixed on glass by the Doctor Blade technique, and on low-density polyethylene (LDPE) by the liquid phase suspension method. The films were characterized by SEM-EDX. The use of doped and undoped photocatalysts fixed in two types of substrates was evaluated in a pilot scale photoreactor under solar radiation. The photoreactor consisted of a simple model designed based on the use of photocatalysts fixed on flat substrates. The adsorption, photodegradation and photolysis processes of methylene blue (MB) were evaluated separately in order to define the extent to which the photocatalyst degraded. The pilot scale system, with the method of fixing the catalyst on a glass substrate, degraded 72.8% of the dye in 6 h, studied under the Langmuir Hinshelwood pseudo-first-order mathematical model with a constant of 0.0024 min−1. With the method of fixing the catalyst on an LDPE substrate, it degraded 68.1% in 6 h, following the same mathematical model, with a constant of 0.0021 min−1.

The uptake of ozone on methane flame soot has been studied in a flow reactor with a mobile insert coupled to a beam-sampling mass spectrometer at T = 256 and 295 K in the range of [O3] = 1.1 × 1012–4.1 × 1013 cm–3. The uptake was found to be multistage. Both the fast and slow stages of the uptake occur by the reaction mechanism on the surface with an adsorbed particle. Based on the Langmuir concept of adsorption, the uptake coefficient can be represented as γ = γ0/(1 + KL[O3]) with the γ0 and KL parameters for the first stage of the uptake γ0(295 K) = (6.6 ± 0.4) × 10–4 and γ0(256 K) = (8.1 ± 2.6) × 10–4, KL(295 K) = (7 ± 1) × 10–14 and KL(256 K) = (22 ± 9) × 10–14 cm3. The same parameters for the second stage are γ0(295 K) = (1.3 ± 0.2) × 10–4 and γ0(256 K) = (1.2 ± 0.5) × 10–4, KL(295 K) = (11 ± 2) × 10–14 and KL(256 K) = (28 ± 13) × 10–14 cm3. The rate constant of the unimolecular decomposition of the surface complex with the adsorbed ozone molecule was evaluated from the dependence of γ on the exposure time of the soot coating to the О3 flow: kr(295 K) = (0.39 ± 0.01) s–1, kr(256 K) = (0.15 ± 0.01) × 10–2 s–1 for the fast stage and kr(295 K) = (2.8 ± 0.1) × 10–2 s–1, kr(256 K) = (1 ± 0.04) × 10–2 s–1 for the slow stage. In the limit of low concentrations, γ depends only weakly on [O3] and T due to the relation γ0 ∼ kr/kd and close values of the activation energy of the reaction rate constant kr and the heat of adsorption of the desorption rate constant kd.

The focus of this research was on the catalytic reduction of nitrate to nitrogen gas for the water conservation. Zero-valent iron (Fe0) with bimetallic catalyst that carrier supported palladium (Pd...

2D reactions on surfaces/interfaces are important but difficult to study. In this issue of Chem, Seki et al. report the use of sum-frequency generation vibrational spectroscopy to elucidate that molecular mechanisms of surfactants facilitated "on-water" 2D polymerization reactions by identifying the key reaction intermediate.

Combined steam and CO2 reforming of methane (CSCRM) testing was used to determine the responses of CH4 conversion, H2 and CO yield, and CO2 conversion at a temperature range of 500–1000 °C, (CO2 + ...

A batch reactor was used to investigate kinetic behaviour of propionic acid with N-butanol over acidic ion-exchange resign SBA-15. The kinetic studies were performed for temperatures ranges 358oK to 388oK then feed varies 1–5 the molar proportions of propionic acid to N-butanol. The response rate was discovered to rise with rising temperature. However, propionic acid equilibrium conversions slightly change the entire reaction temperature suggesting this reaction's impact is negligible. It’s been discovered that propionic acid conversion improves with feed molar ratios rising from 1 to 5. Based on the outcomes of binary adsorption studies, relative sorption between two interacting species is determined. Water > n-butyl propionate > propionic acid > n-butanol follows the severity of adsorption strengths. The kinetic information was associated Langmuir Hinshelwood Haugan Watson models to assess kinetic variables for each model, respectively. The LHHW has produced the highest outcomes among these researched models.

В данной статье представлены данные по физико-химическому исследованию гетерогенного рутений содержащего катализатора Ru/СПС MN 100. Представлена важность таких исследование для изучения каталитических реакций, для установления возможного механизма реакции гидрирования, а так же как дополнения при кинетических исследованиях. В статье катализатор исследован методом низкотемпературной адсорбции азота, хемосорбции водорода, просвечивающей электронной микроскопии (ПЭМ) и рентгенофотоэлектронной спектроскопии (РФЭС). Метод низкотемпературной адсорбции азота позволил установить, что катализатор характеризуется развитой внутренней удельной поверхностью (726 м/г по модели БЭТ) и характеризуется значительной мезопористостью, при этом наибольший диаметр пор составляет около 3.6 нм. Удельная площадь поверхности активного металла - Ru, по данным метода хемосорбции водорода, составляет 1 м/г. Рутений содержащие частицы распределены по всему объему носителя, при этом они способны образовывать небольшие агрегаты и характеризуются различной степенью кристалличности. Установлен элементный состав поверхности катализатора; Ru имеет различные степени окисления. На основании полученной ранее математическая модель процесса и проведенных физико-химических исследований катализатора предположена модель Ленгмюра-Хиншельвуда для описания механизма реакции жидкофазного каталитического гидрирования моно- и дисахаридов. This article presents data on the physical and chemical study of heterogeneous ruthenium-containing catalyst Ru/SPS MN 100. The importance of such studies for the study of catalytic reactions, for establishing the possible mechanism of the hydrogenation reaction, as well as additions in kinetic studies is presented. In this paper, the catalyst was studied by low-temperature nitrogen adsorption, hydrogen chemisorption, transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS). The method of low-temperature nitrogen adsorption allowed us to establish that the catalyst is characterized by a developed internal specific surface (726 m/g according to the BET model) and is characterized by significant mesoporicity, with the largest pore diameter of about 3.6 nm. The specific surface area of the active metal - Ru, according to the method of hydrogen chemisorption, is 1 m/g. Ruthenium containing particles are distributed over the entire volume of the carrier, while they are able to form small aggregates and are characterized by different degrees of crystallinity. The elemental composition of the catalyst surface has been determined; Ru has different oxidation States. Based on the previously obtained mathematical model of the process and physical and chemical studies of the catalyst, the Langmuir-Hinshelwood model is proposed to describe the reaction mechanism of liquid-phase catalytic hydrogenation of mono - and disaccharides.

The crystallite size effects of Pt nanoparticles on the CeO2 (Pt/CeO2) prepared with four different Pt precursors were investigated in terms of their thermal stability and catalytic activity for a water-gas shift (WGS) reaction using the compositions of reformates after a typical steam reforming of propane. The Pt/CeO2 prepared with a diamine dinitroplatinum (Pt(NO2)2(NH3)3) precursor, which forms the cationic Pt(NH3)22+ species on the negatively-charged CeO2 surfaces, revealed a superior catalytic activity and thermal stability by forming the partially oxidized smaller Pt nanoparticles decorated with metallic Pt surfaces as well as by forming the strongly interacted PtOx-CeO2 interfaces. The stable preservation of the pristine smaller Pt nanoparticles with small aggregations even under the hysteresis test from 250 to 400 °C was mainly attributed to the strong metal-support interactions. The optimized Pt/CeO2 was further studied to obtain kinetic equations derived by Langmuir-Hinshelwood (LH) model, and the optimal operating conditions of WGS reaction were found to be ~280 °C and H2O/CO molar ratio of 9 with the activation energy of ~78.4 kJ/mol.

Glucose solar light photoinduced oxidation on Bi2WO6 and the chemical kinetics conditions for concurrent photoelectrochemical H2 production are reported. The results show that the conversion of this organic compound is determined by their surface concentration according to the Langmuir-Hinshelwood mechanism. The performance of Bi2WO6 powder for the photocatalytic oxidation of glucose is higher than that observed with TiO2-based materials. Glucose degradation and mineralization rates are similar; therefore, stable intermediates are not formed during glucose oxidation. Photoluminescence studies indicate that glucose promotes electron injection into the valence band of semiconductor. The initial glucose concentration in combination with the electrode potential used, determines the H2 production. In fact, electrode potential of 0.9 V vs. SHE and 60 ppm of glucose defines kobs values equal to kK with maximum H2 evolution rate: 3.05 μmol h−1 cm−2. This value arises from the transformation of the 97% of the Faradaic current measured. The phenomenological conditions for renewable energy applications have been envisaged.

An important category of glycerol derivatives, having multiple practical applications, are its esters with acetic acid (acetates or acetins). The most common preparation method of glycerol acetates is the direct esterification of glycerol with acetic acid in presence of acid catalysts. In this work is investigated the liquid phase glycerol esterification with acetic acid, catalyzed by the commercial Purolite CT-275 ion exchange resin. In this aim, there were performed batch experiments, in a stirred autoclave reactor, at initial acetic acid to glycerol molar ratios between 4 and 9 and temperatures between 70 and 110 °C. The experimental data were used to develop a kinetic model, based on the Langmuir Hinshelwood theory. The components activities, involved in the calculation of the reaction rates, were evaluated by the UNIFAC Dortmund method. The proposed kinetic model predicts with good accuracy the products distribution dependencies on the reactants molar ratio and reaction temperature. The calculated values of the Weisz-Prater criteria evidenced influences of the internal diffusion on the esterification process kinetics, over an initial reaction time interval. The proposed kinetic model is directly utilizable in the commercial process analysis and design calculations.

Reduced graphene oxide (RGO) were successfully prepared through chemical reduction of GO that was prepared by modified Hummer’s method. Characterization of GO and RGO was performed using different techniques and they were trapped in acrylic acid (PAAc) and polyvinyl alcohol (PVA) to form (PVA/PAAc)–GO and (PVA/PAAc)–RGO nanocomposites using gamma irradiation technique. Characterization the prepared nanocomposite was investigated using X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and transmission electron microscopy (TEM). TiO2 was also trapped in the nanocomposite matrix to perform (PVA/PAAc)–GO–TiO2 and (PVA/PAAc)–RGO–TiO2 nanocomposite hydrogels. It was found that the crystallite size of (PVA/PAAc)–TiO2, (PVA/PAAc)–GO–TiO2 and (PVA/PAAc)–RGO–TiO2 nanocomposite calculated using Debye–Scherrer’s equation are 52.8, 26.02, and 23 nm, respectively. The surface morphology explained a good dispersion of GO within (PVA/PAAc)–GO–TiO2 and (PVA/PAAc)–RGO–TiO2 appears as a porous structure. The photocatalytic activity of the obtained nanocomposites was tested for the photodecolorization of direct blue 71 dye (DB71) in the aqueous medium under UV light. A complete decolorization of DB71 was achieved after 40 min at pH 6 in the presence of 2 mL/L hydrogen peroxide. The rate of photodecolorization follows Langmuir Hinshelwood pseudo-first-order kinetics. It was also obtained that (PVA/PAAc)–RGO–TiO2 nanocomposites can be reused for ten times with full activity.

The photocatalytic activity of TiO2 and ZnO based catalysts, which is based on their ability to generate electron–hole pairs upon photoillumination is limited due to their wide band gaps and lack of efficient retrievability post-application. This work reports on the fabrication, characterisation and comparison of electrospun TiO2 and ZnO nanofibers when bare vs when functionalised with a phthalocyanine. The generated photocatalysts are attractive because they absorb visible light and are easily retrievable and hence reusable. With the Pc anchored onto their surfaces, the anatase TiO2 nanofibers and the wurzite ZnO nanofibers possessed singlet oxygen quantum yields of 0.22 and 0.16 in water, respectively. Evaluation of the photocatalytic efficiencies of the nanofibers was conducted by studying the photodegradation of methyl orange. The Pc decorated nanofibers were found to be more effective photocatalysts than the bare ones with the phthalocyanine TiO2 nanofibers being the best. The degradation kinetics were found to follow pseudo first order kinetics and obeyed the Langmuir Hinshelwood model. The nanocatalysts reported herein are therefore feasible candidates for real-life water purification applications.

In this paper, the modelling, numerical lumping and simulation of the dynamics of one-dimensional, isothermal axial dispersion tubular reactors for single, irreversible reactions with Power Law (PL) and Langmuir-Hinshelwood-Hougen-Watson (LHHW)-type kinetics are presented. For the PL-type kinetics, first-order and second-order reactions are considered, while Michaelis-Menten and ethylene hydrogenation or enzyme substrate-inhibited reactions are considered for the LHHW-type kinetics. The partial differential equations (PDEs) developed for the one-dimensional, isothermal axial dispersion tubular reactors with both the PL and LHHW-type kinetics are lumped to ordinary differential equations (ODEs) using the global orthogonal collocation technique. For the nominal design/operating parameters considered, using only 3 or 4 collocation points, are found to adequately simulate the dynamic response of the systems. On the other hand, simulations over a range of the design/operating parameters require between 5 to 7 collocations points for better results, especially as the Peclet number for mass transfer is increased from the nominal value to 100. The orthogonal collocation models are used to carry out parametric studies of the dynamic response behaviours of the one-dimensional, isothermal axial dispersion tubular reactors for the four reaction kinetics. For each of the four types of reaction kinetics considered, graphical plots are presented to show the effects of the inlet feed concentration, Peclet number for mass transfer and the Damköhler number on the reactor exit concentration dynamics to step-change in the inlet feed concentration. The internal dynamics of the linear (or linearized) systems are examined by computing the eigenvalues of the linear (or linearized) lumped orthogonal collocation models. The relatively small order of the lumped orthogonal collocation dynamic models make them attractive and useful for dynamic resilience analysis and control system analysis/design studies.

Herein we report the performance of cheaper, more efficient and eco-friendlier chitin (CN) and chitosan (CS) biopolymers supported Cu nanoparticles (Cu NPs) catalysts (1.5 wt% Cu/CN) and (4.5 wt% Cu/CS) in the reaction model of para-nitrophenol (p-NP) reduction to para-aminophenol (p-AP) by NaBH4. The catalysts were synthetized with impregnation method and CN was extracted from local shrimp shells wastes, while CS was obtained by the deacetylation of CN. It was found that the activity of 1.5 wt% Cu/CN, with a lower Cu loading, is better than that of 4.5 wt% Cu/CS, which achieved 100% p-NP conversion to p-AP in short reaction times at all studied reaction temperatures. The activity of each catalyst was found to depend on the interaction modes of Cu NPs with the functional groups of CN and CS, which affects the textural parameters of the catalysts and the dispersion of Cu NPs, as revealed by various characterization techniques used. Kinetic of p-NP reduction was found to follows the pseudo-first order with respect to p-NP concentration. The apparent rate constants at T = 25 °C were calculated to be kapp = 0.854 min−1 and 0.350 min−1 for 1.5 wt% Cu/CN and 4.5 wt% Cu/CS catalysts, respectively, which increased with the reaction temperature. Kinetics data of p-NP reduction at T = 25 °C, obtained for various concentrations of reagents, were successfully modeled using the Langmuir–Hinshelwood mechanism. The related kinetic parameters such as the adsorption equilibrium constants K(p-NP), K( $${\text{BH}}_{4}^{ - }$$ ) and the surface rate constant, k, were calculated. The competitive adsorption between p-NP and $${\text{BH}}_{4}^{ - }$$ was shown to control the rate of p-NP reduction to p-AP.

The synthesis of γ-valerolactone (GVL), a platform molecule that can be produced from lignocellulosic biomass, was performed in this work by hydrogenation of an alkyl levulinate over Ru/C. Kinetic models reported in the literature are typically not compared with rival alternatives, even if a discrimination study is needed to find the optimum operating conditions. Different surface reaction kinetic models were thus considered in this work, specifically addressing hydrogenation of butyl levulinate to GVL, where the latter was used as a solvent to minimize potential solvent interference with the reaction, including its evaporation. The Bayesian approach was applied to evaluate the probability of each model. It was found that non-competitive Langmuir-Hinshelwood with no dissociation of the hydrogen model has the highest posterior probability.

The kinetics of condensation reaction of methoxyacetone with 2-methyl-6-ethyl aniline catalyzed by NKC-9 cation exchange resin was studied for the first time. The reaction temperature of Schiff base synthesis was determined in the range of 367.15 to 401.15 K by the batch experiments, and influences of reactant molar ratio, temperature, catalyst dosage, and particle size on the ultimate conversion were also studied. The dynamic data were used to be relevant with PH, ER(1), ER(2), and Langmuir Hinshelwood Hougen Watson homogeneity models. Model parameters, including reaction equilibrium constants, activation energy, enthalpy change, entropy change, and rate constants, were solved. The accuracy of the model was validated by means of both experimental proofs and standard deviation between the predicted and experimental data. Finally, a series of characterization tests such as Fourier transform infrared spectroscopy, X-ray diffraction, and polarizing microscopy were performed to investigate the structure and properties of NKC-9.

Bismuth ferrite (BiFeO3) is considered as one of the most promising materials in the field of multiferroics with great potentials in photocatalysis due to their excellent properties of relatively small band gap, stable structures, and low cost. In this work, a facile green route was successfully used for the fabrication of high-purity yttrium-doped and undoped bismuth ferrite (BiFeO3) nanoparticles. κ-carrageenan seaweed was used as a biotemplate for the construction of the material. The obtained products were characterized and the photocatalytic effect of doped and undoped BiFeO3 were evaluated on the degradation of methylene blue (MB) under direct sunlight. The formed particles are in the range of 80–90 nm that exhibited morphology of rhombohedral perovskite structure as confirmed by FESEM and HRTEM analysis. Decreasing of band gap energy from 2.07 eV to 2.05 eV as the concentration of yttrium dopant increased significantly affected their photocatalytic behaviour. There was a remarkable improvement in the photocatalytic activity of 1% of yttrium-doped BiFeO3 towards the decomposition of methylene blue (MB) under direct sunlight irradiation. This was attributed to the strong absorption of visible light and the effective separation of photoinduced e− and h + pair, as compared to the pristine BiFeO3. In addition, the influence of operational parameters on the removal efficiency of MB, such as catalyst dosage and initial dye concentrations, was optimized as a function of time. The kinetics of the photocatalytic MB removal was later found to follow Langmuir Hinshelwood model.

This research work was carried out with the objective of understanding the reaction kinetics involving different catalysts like SrTiO3 (STO), sulfur doped SrTiO3 (S-STO), Ag metalized SrTiO3 (Ag-STO) and Ag metalized sulfur doped SrTiO3 (Ag-S-STO) which possess unique surface and bulk characteristics. Each catalyst was modified and improved by either bulk lattice modification or surface modification by metallization or by both the above process and the obtained results were compared with pristine SrTiO3. Though the nature of each catalyst was different, the photocatalytic degradation reaction taking place on their surface was found to fit for first order reaction only by 50% whereas, the reaction fitted well with the zero order reaction process. Ag-S-STO sample shows excellent photocatalytic activity under the illumination of solar light compared to the other catalysts. This activity can be correlated to the bulk / surface lattice modification by sulfur and also to the SPR effect of metallized silver particles. The photocatalytic degradation reaction rate was further enhanced in the presence of H2O2 as an oxidizing agent due to the formation of highly reactive species like hydroxyl free radicals and peroxy radicals. The reaction was found to follow bimolecular Langmuir Hinshelwood mechanism. The degradation reaction mechanism was proposed based on the intermediates detected by HPLC technique during the reaction process.

The presence of diclofenac (DCF) in water has developed into a severe environmental problem due to its pernicious effects on animals and human being. Herein, a photoelectrocatalytic (PEC) method using I doped TiO2 (I-TiO2) photoelectrode has been developed, which exhibited excellent visible activity in the degradation of DCF as well as pharmaceutical wastewater. The Langmuir Hinshelwood kinetic model, active species trapping experiments and analysis of intermediate products were employed to analyze the PEC degradation mechanism of DCF. The results revealed that the decomposition of DCF was primarily performed on the photoelectrode (I-TiO2) surface, and the degradation process was accompanied by the dechlorination reaction. The degradation of DCF was caused mainly by holes (66.6%) and hydroxyl radicals (27.6%) when Na2SO4 acted as electrolyte. The degradation rate of DCF could be significantly enhanced under the condition of high Cl− concentration (NaCl acted as electrolyte), which was caused by the participation of chloride radicals (Cl ) in the PEC process. The Cl was the major factor contributing to the decomposition of DCF, and the holes and hydroxyl radicals played a less important role than Cl under this condition.

In this study, HZSM-5(1) and HZSM-5(2) zeolites were prepared with Al(NO3)3 and Al(OH)3 sources, respectively. Kinetic modeling of liquefied petroleum gas (LPG) cracking over synthesized HZSM-5 zeolites with different framework aluminum (Al) locations was investigated at 500–650 °C using Langmuir–Hinshelwood–Hougen–Watson theory. In a proposed LPG cracking mechanism, 26 elementary surface reaction steps including C–H and C–C protolytic cracking, hydrogen transfer, isomerization and absorption–desorption of olefins and also 2 lumped reactions for C5+ formation, were considered. Due to the existence of numerous local optimal points, genetic algorithm was employed. The estimation of kinetic parameters was performed by minimizing the mean of the sum of squares between theoretical and experimental data.

In recent years, the discovery of efficient catalyst with low price to sulfur dioxide (SO2) oxidation in normal temperature is a major concern in the industry. In present study, in first step the boron nitride nanotube (BNNT) with Ge were adopted and the surface of Ge-adopted BNNT via O2 molecule were activated. In second step the SO2 oxidation on activated Ge-BNNT surface via Langmuir Hinshelwood (LH) and Eley Rideal (ER) mechanisms was investigated. Results show that O2 activated Ge-BNNT surface can oxide the SO2 molecule via Ge-BNNT-O-O* + SO2 → Ge-BNNT-O-O*-SO2 → Ge-BNNT-O* + SO3 and Ge-BNNT-O* + SO2 → Ge-BNNT + SO3 reactions. Results show that SO2 oxidation on activated Ge-BNNT surface via the LH mechanism has lower energy barrier than ER mechanism. Finally, calculated parameters reveal that activated Ge-BNNT is acceptable catalyst with low price and high performance for SO2 oxidation in normal temperature.

To accelerate the reaction of hydration of fumaric acid (F) to produce malic acid (M), Montmorillonite K10 (MK10) was tested as a solid acid catalyst. The experiments were performed in a stirred pr...

The discovery of acceptable catalysts to oxidation of the silicon monoxide (SiO) and nitrogen (N2) molecules has high importance. In present study, the C60 and B36N36 nanocages with Sn and Ge were adsorbed, respectively and then surfaces of Sn C60 and Ge B36N36 via O2 were activated. In this study, the oxidation of the SiO and N2 molecules on surfaces of the Sn C60 and Ge B36N36 via the Langmuir Hinshelwood (LH) and Eley Rideal (ER) mechanisms was investigated, respectively. Results showed that the Sn C60 and Ge B36N36 can oxidize the SiO and N2 molecules via C60 Sn + SiO + O2 → C60 Sn O + SiO2 and B36N36-Ge + N2 + O2 → B36N36-Ge O + N2O reactions, respectively. Results showed that the oxidation of SiO and N2 on surfaces of Sn C60 and B36N36-Ge nanocages via the LH mechanism has lower energy barrier than ER mechanism. Finally, results revealed that the Sn C60 and B36N36 Ge nanocages are acceptable catalysts to oxidation of SiO and N2 molecules with high performance.

Novel polystyrene-poly(N-isopropylmethacrylamide-acrylic acid) [PSTY-PNIPMA-ACC] core-shell micro particles were prepared by seed induced emulsion polymerization. Nano-Ag-PSTY-PNIPMA-ACC composite particles were synthesized by reduction of AgNO3 salt with reductant NaBH4 in the presence of water as medium and micro particles as template. The pure and composite micro particles were characterized by various techniques such as UV-visible spectroscopy (UV-vis) and Fourier transform infrared spectroscopy (FTiR) to illustrate their optical properties and structural hierarchies, respectively. Dynamic light scattering (DLS) analysis was performed to study the particles size distribution. TEM analysis shows that Ag NPs were monodispersed and equally distributed in spherical shaped shell of PSTY-PNIPMA-ACC micro particles. The prepared nano-Ag-PSTY-PNIPMA-ACC particles were used as catalyst in reduction of Rhodamine B (Rh-B) using NaBH4 as reductant. For comparative analysis, reduction of Rh-B was also performed in absence of nano-Ag-PSTY-PNIPMA-ACC catalyst and in the absence of NaBH4, respectively. Rh-B was only reduced in short time at feasible rate in presence of both composite micro particles and NaBH4. Degradation of Rh-B followed the pseudo first order kinetics and values of apparent rate constant (kapp) were come out to be 1.127 and 0.004min−1 with percentage degradation of 99.03 and 4.37%, respectively. Results showed that our prepared nano-Ag-PSTY-PNIPMA-ACC particles are promising catalysts. High catalytic activity of composite micro particles may be attributed to their core-shell type morphology, sieved shell, small sized Ag NPs restricted in shell region. Langmuir Hinshelwood mechanism was followed by degradation of dye. Optimum concentration for maximum degradation of Rh-B in small time interval was found 4.95 mM. Various other toxic dyes such as brilliant blue (Bb) and methylene blue (MB) were also reduced individually and simultaneously under same reaction conditions.

Highly effective tungsten-based carbon nanotubes (W/CNT) were synthesized and used as a heterogeneous catalyst for the oxidation of dibenzothiophene (DBT) with the oxidant H2O2. The obtained materials were characterized by modern methods. The Langmuir–Hinshelwood kinetics model described the precursor mechanism of the reaction well through an intermediate compound. The low activation energy showed that the reaction was mainly controlled by diffusion. The positive activation enthalpy proved the endothermic nature of the activation process, and this process did not alter the inside structure of the catalyst. The thermodynamic parameters of the reaction were determined, which implied that the oxidation was endothermic and spontaneous at 303 K. The more negative values of the Gibbs free energy from 283 to 323 K confirmed that the reaction was more favorable at high temperatures. The stability and activity of catalyst were retained after three reaction cycles.

Catalytic reactions on surfaces with forced oscillations in physical or electronic properties undergo controlled acceleration consistent with the selected parameters of frequency, amplitude, and external stimulus waveform. In this work, the general reaction of reversible A-to-B chemistry is simulated by varying the catalytic (heat of reaction, transition state and intermediate energies) and oscillation parameters (frequency, amplitude, endpoints, and waveform) to evaluate the influence on the overall catalytic turnover frequency and steady state extent of conversion. Variations of catalytic cycle energies are shown to comprise a superVolcano of superimposed individual Balandin–Sabatier volcano plots, with variations in linear scaling relationships leading to unique turnover frequency response to forced oscillation of the catalyst surface. Optimization of catalytic conditions identified a band of forced oscillation frequencies leading to resonance and rate enhancement as high as 10 000× above the static Sabatier maximum. Dynamic catalytic reactions conducted at long times achieved oscillatory steady state differing from equilibrium consistent with the imposed surface oscillation amplitude acting as a ‘catalytic pump’ relative to the Gibbs free energy of reaction.

Present article reports for the first time a simple, eco-friendly synthesis of nano TiO2 semiconductor photocatalyst mediated by ethanolic Tamarindus indica leaf extract using titanium isopropoxide as precursor. XRD of the obtained product confirms the synthesis of anatase titania. Presence of aggregates of near spherical particles of size range 20–40 nm was revealed by SEM and TEM images. Purity of synthesised titania was verified by EDX and the surface area of the product determined by BET was 75 m2/g. The band gap estimated by UV spectroscopy was 3.21 eV. The photocatalytic activity of synthesised nano TiO2 was tested on photodegradation of Titan yellow dye by heterogeneous semiconductor photocatalysis process. The effect of TiO2 loading (0.25–1.0 g/l), initial concentration of Titan yellow (10–40 ppm), pH (3, 5, 7, 9 and 11) of the dye on photodegradation was studied in presence of UV light of 125 W. The percent degradation observed for 10 ppm dye at nano TiO2 loading of 0.75 g/l at pH 7.0 was 95% in 120 min. Effect of various light source and irradiation time were also studied. The degradation data was best fitted by Langmuir Hinshelwood kinetics with apparent rate constant of 0.015 min−1. The photo degradation follows the pseudo first order kinetics.

This study presents the synthesis of a novel Mn2+ and Co2+ co-doped TiO2 (Mn-Co-TiO2) for the photocatalytic degradation of enoxacin (ENX) under solar light irradiation. The as-synthesized photocatalysts were fully characterized by X-ray diffraction (XRD) analysis, field emission-scanning electron microscopy (FE-SEM), and UV-diffuse reflectance spectroscopy (UV-DRS). The structural appearance of the Mn-Co-TiO2 suggests porous cylindrical type morphology. Moreover, the co-doping of Mn2+ and Co2+ has successfully reduced the band gap of TiO2 from 2.81 eV to 2.10 eV. Applying Langmuir Hinshelwood kinetic model, the photocatalytic degradation of ENX by Mn-Co-TiO2 followed pseudo-first-order kinetics. A total of twelve (12) DPs of ENX were identified by UPLC/MS-MS. The natural water constituents such as CO32−, HCO3−, Cl− and Fe3+ had great influence on the photocatalytic degradation of ENX by Mn-Co-TiO2 under solar light irradiation. The as-synthesized Mn-Co-TiO2 showed appreciable results for the photocatalytic degradation of ENX in synthetic wastewater (SWW) and real wastewater (RWW) samples. Furthermore, the toxicity assessment of ENX and its DPs towards aquatic organisms (i.e., fish, daphnia and green algae) was measured which are helpful for the practical implementation of this technology for wastewater treatment. The Mn-Co-TiO2 materials also showed good peroxidase-like activity towards the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 and followed Michaelis-Menten kinetics.

Though photocatalytic reactions gather enormous attention, dependences of light intensity and reactant concentration have not been concurrently expressed clearly. In the previously reported studies, a quadratic formula equation obtained from the conventional analysis using the concentration of electron–hole pairs has been modified. In this report we numerically simulated the reaction with a two-dimensional(2D)-ladder kinetics without using electron–hole concentrations. In this kinetics, the rates of four fundamental processes, (i) photoabsorption, (ii) reduction, (iii) oxidation, and (iv) recombination, were treated as the transitions between the states of each powder characterized by the numbers of possessing negative and positive charges. Through the numerical 2D-ladder simulation with various rate constants, the light-intensity (I) dependence of the oxidation rate was found to be fully expressed by involving the square of the intrinsic quantum yield into the square root part of the well-known quadratic...

Recently the investigation of single atom catalyst is greatly focused for the sequestration of toxic CO from the atmosphere. In this study, we explored the reaction mechanisms and activation barriers for the CO oxidation over the Al-decorated C24N24 fullerene (Al@C24N24) using density functional theory. The results shows that Al incorporation in C24N24 is energetically desirable and is the active site for the catalytic reactivity. The CO and O2 molecules are strongly adsorbed over the Al atom. Two possible reaction pathways are investigated for the CO oxidation, i.e., the Langmuir Hinshelwood (LH) and Eley Rideal (ER). Comparison of the barrier energies shows that the oxidation reaction moves fast through the ER mechanism. Moreover, the CO + O* reaction proceeds quickly over the Al@C24N24 surface, without the need of any energy barrier, indicating the high catalytic activity of the studied catalyst. These results show that the designed catalyst may be helpful to synthesize novel noble metal free catalysts to eliminate the fatal CO gas from the atmosphere.

Biodiesel is known as the best candidate for the replacement of nonrenewable biodiesel. Currently, it has been produced from transesterification and esterification of triglycerides and fatty acids, respectively. However, the production of biodiesel from waste oils surrounded by numbers of obstacle such as saponification problem, complex purification process, high-cost production, and dual-step processes has made them the least choice feedstock. Recently, an advanced scientific finding in the catalysis technology has been reported for the reduction of free fatty acid (FFA) from waste oils. Photocatalysis is a light-induced catalytic process that involves oxidization and/or reduction of organic molecules via redox reactions activated through the electron-hole pair generated on the surface of semiconductors upon light irradiation. The esterification of FFA with ethanol is carried out according to the Langmuir Hinshelwood reaction path: when a photocatalyst is irradiated by ultraviolet light, the photogenerated electrons (e−) in the valence band are excited and transferred to the conduction band, and the same number of holes (h+) will be produced. The methanol adsorbed on the catalyst surface reacts with photogenerated hole (h+) to generate H+ and radical methanol. At the same time, fatty acid molecules adsorbed on the surface of the catalyst is reduced to form free radical by accepting the photogenerated electron (e−) on the surface. Then, the reaction between radicals and protons will react to form methyl ester and water. In this chapter, we successfully studied, analyzed, and discussed the classical technique of biodiesel production, and fundamental, theories, concept, and potential of advanced photocatalysis technology in the biodiesel production.

International audience; This work presents a solution for the photocatalytic degradation of the antibiotic ciprofloxacin (CIP) in water, without using P25 TiO2 powder and thus getting rid of expensive separation steps. It consists in using a TiO2 coating that is directly deposited on the optical window of a photocatalytic micro-reactor and 365 nm UV LEDs as radiation source. P25 TiO2 powder was also studied as reference. HPLC-MS was used to determine the transformation products and the pathways reactions. CIP was slowly degraded by the photolysis reaction at 365 nm: (75 % removal after 8 h of UV irradiation). However, no significant decrease of the total organic carbon (TOC) was noticed, thus showing the presence of transformation products not degraded by the action of UV-light alone. For a low catalyst amount (i.e 0.12 g of TiO2, whatever the form, powder or coating, per liter of contaminated water,), excellent CIP degradation by photocatalysis was observed. Complete CIP degradation after 1 h of irradiation was required using P25 and 8 h using TiO2 coating. Different preferential reaction pathways were identified for both TiO2 catalysts. The Langmuir-Hinshelwood model showed a very good representation of the kinetics, unlike its simplified pseudo-first order model. Photocatalysis experiments did not show a complete mineralization (60–70 % of TOC removal), but most of the aromatic transformation products were degraded. The last transformation products were identified as small aliphatic acids. There is therefore a real interest in using MOCVD coating of TiO2 for sustainable wastewater treatment to avoid expensive catalyst separation. A study with a spiked real effluent from a wastewater treatment plant was performed and a satisfactory degradation was obtained. Slower kinetics were found due to the presence of additional organic products and scavenger compounds such as HCO3-.

Use of heterogeneous biosensors in microfluidic channels for diagnostic and detection of diseases in early stages is a novel, relatively cheap and applicable solution for saving lives and health purposes. It has attracted great interest in experimental field and a lot of works are being done in order to reach better biosensors with reliable results and fast detection. A comprehensive numerical model of Langmuir-Hinshelwood mechanism would help speeding up the process of design and analysis of biosensors. For this means we have developed a code in Fortran to simulate flow inside a microfluidic channel combined with Langmuir-Hinshelwood reactions on the surface of the biosensor. Control-volume based finite-element method (CVFEM) with high order discretisation has been used to solve full Navier-Stokes equations with chemical reactions on the biosensor. Results has been validated with existing experimental data from literature. The influence of target concentration as well as the inlet velocity (flow rate replica) on the biosensor saturation time, moreover, investigated in this study. The results show that as the inlet velocity and concentration increases the time that concentration on the surface of biosensor reaches its asymptotic value decreases, although increase in inlet velocity does not have any effect on dissociation stage of binding cycle.

A jointed experimental and theoretical investigation pointing out new insights about the microscopic mechanism of the volatile organic compounds (VOCs) photocatalytic elimination by TiO2 was done. Methane, hexane, isooctane, acetone and methanol were photomineralized in a batch reactor. Values of K (adsorption constant on TiO2) and k (mineralization rate constant) of the five VOCs (treating the kinetic data through a Langmuir–Hinshelwood approach) were determined. Recorded K (in the range of 0.74 × 10−2–1.11 × 10−2 ppm−1) and k (in the range of 1.9–9.9 ppm min−1) values and performed theoretical calculations allowed us to suggest the involvement of an electron transfer step between the VOC and the hole, TiO2(h+), as the rate-determining one.

The self-condensation and cross-condensation reactions of ethanol and isoamyl alcohol are examined to better understand the potential routes to value-added byproducts from fuel ethanol production. Reactions have been carried out in both batch autoclave and continuous condensed-phase reactors using a lanthanum-promoted, alumina-supported nickel catalyst at near-critical condensed phase conditions. Analysis of multiple candidate kinetic models led to a Langmuir&ndash, Hinshelwood rate expression that is first-order in alcohol with water as the strongly adsorbed species. This model provides the best fit of data from both batch and continuous reactor experiments. Activation energies for primary condensation reactions increase as carbon chain lengths increase. Selectivities to higher alcohols of 94% and 87% for ethanol and isoamyl alcohol, respectively, were observed at different operating conditions.

As a byproduct of the physical refinement of crude palm oil, palm fatty acid distillate or PFAD has a potential to be transformed into monoglycerides by means of irreversible esterification with glycerol over a cation exchange resin catalyst. Irreversibility of the esterification can be assured by continuous azeotropic removal of water by adding xylene as an entrainer. Because PFAD-glycerol esterification demands high temperatures for fast conversion and high selectivity of monoglycerides, it is necessary to test catalyst reusability performance. In this research, evaluation of catalyst reusability performance was based on five parameters: free fatty acid conversion, the rate of free fatty acid decomposition, the selectivity of monoglycerides, monoglyceride concentration, and the cation exchange capacity of the catalyst. The cation exchange resin used was Tulsion T-42 SM. The evaluation was conducted using the simple multi-attribute rating technique extended to ranking (SMARTER) method. The results showed that the optimum reaction temperature was 180°C. Ultimately, a kinetic study at 180°C was also performed to model the reaction after using similar catalysts for certain times. This kinetic study revealed that the reaction mechanism changed from Langmuir-Hinshelwood to Eley-Rideal after several cycles of catalyst reuse.

In this preprint, we reevaluate the use of X-ray photoelectron spectroscopy (XPS) to determine substitution levels of reactions on non-oxidized silicon surfaces. XPS is the most commonly used method to determine the yields of reactions on surfaces. We go back to the most basic assumptions, and work through the calculations to provide a revised set of calculations that take into account (i) possible adventitious hydrocarbon contamination, (ii) the effect of choosing a different silicon crystal face [Si(100) versus Si(111)], and (iii) the utility of choosing a small heteroatom tag to enable a more accurate measure of substitution levels. We provide a simple algorithm and summary of the equations one can use to make it easy for the reader/researcher.

Desorption/Ionization Induced by Neutral SO2 Clusters (DINeC) is employed as a very soft and efficient desorption/ionization technique for mass spectrometry (MS) of complex molecules and their reactions on surfaces. DINeC is based on a beam of SO2 clusters impacting on the sample surface at low cluster energy. During cluster-surface impact, some of the surface molecules are desorbed and ionized via dissolvation in the impacting cluster; as a result of this dissolvation-mediated desorption mechanism, low cluster energy is sufficient and the desorption process is extremely soft. Both surface adsorbates and molecules of which the surface is composed of can be analyzed. Clear and fragmentation-free spectra from complex molecules such as peptides and proteins are obtained. DINeC does not require any special sample preparation, in particular no matrix has to be applied. The method yields quantitative information on the composition of the samples; molecules at a surface coverage as low as 0.1 % of a monolayer can be detected. Surface reactions such as H/D exchange or thermal decomposition can be observed in real-time and the kinetics of the reactions can be deduced. Using a pulsed nozzle for cluster beam generation, DINeC can be efficiently combined with ion trap mass spectrometry. The matrix-free and soft nature of the DINeC process in combination with the MSn capabilities of the ion trap allows for very detailed and unambiguous analysis of the chemical composition of complex organic samples and organic adsorbates on surfaces.

Developing new high efficiency and stable catalysts for the degradation of organic compounds in effluents, under solar light has been a great challenge. In this regard, this work describes the synthesis of a α-Fe2O3/Nb2O5 mixed oxide by the Pechini method. The results of XRD and SEM/EDS confirmed the presence of Fe and Nb in the materials synthesized. The mixture of semiconductors oxides resulted in the material of greater specific surface area. The catalyst efficiency was verified through the photodegradation of methylene blue (MB) by the heterogeneous photo-Fenton reaction, under different experimental conditions using a 24 factorial experimental design with the central point in triplicate. The variables that most influenced the system response were the concentrations of MB, of the catalyst and of H2O2. The mechanism proposed followed Langmuir-Hinshelwood kinetics, with the greatest color removal percentage of 85%, under the optimal experimental conditions found. The mixed oxide exhibited greater efficiency when compared to the pure oxides synthesized since the synergic effect resulting from the mixture between Fe and Nb oxides led to the hematite activation. The catalyst remained stable even after five consecutive reaction cycles, unlike Nb2O5, suggesting its potential application in the environmental pollutants treatment.

If theory is to be able to predict the rates of catalytic reactions over extended ranges of temperature and pressure, it must provide accurate rate constants for elementary reaction steps, includin...