Initial Rate Method Research Articles

Ethanol Steam Reforming over Rh(1%)MgAl2O4/Al2O3: A Kinetic Study

A kinetic study of ethanol steam-reforming reaction on Rh catalyst supported over a spinel structure (MgAl2O4/Al2O3) was carried out. From the analysis of products distribution, the following four reactions were proposed as the reaction scheme: C2H5OH → CO + CH4 + H2 (ED), C2H5OH + H2O → CO2 + CH4 + 2H2 (ER), water−gas shift reaction, and methane steam-reforming reaction. When the initial rate method was applied, it was demonstrated that in the rate-determining step (RDS) two active sites of the same type are involved. With use of our experimental results and data obtained from the literature, a sequence of 14 elementary steps were proposed, in agreement with the reaction scheme. Taking into account both the reaction mechanism and the occurrence of two active sites in the RDS, four different kinetic expressions can be formulated in which the RDS is (1) dissociative adsorption of ethanol, (2) dehydrogenation of ethoxide, (3) C−C bond scission, or (4) reaction between two adsorbed species. Finally, when discrimination models were applied, it was verified that the mechanism that fits experimental data is that in which the RDS is the surface reaction.

Kinetic investigation of redox reaction between vitamin C and ferric chloride hexahydrate in acidic medium

The kinetics of the reaction between vitamin C (l-ascorbic acid) and ferric chloride hexahydrate was investigated in acidic medium at pH 3 spectrophotometrically. The order of the reaction was established by applying different methods, such as initial rate method, integration method and half-life method. The results obtained from each method were correlated with each other and consistency in all methods was observed. The order of the reaction with respect to each reactant was found first and the overall second order was recommended for the reaction.

Kinetics of reduction of hexavalent neptunium by nitrous acid in solutions of nitric acid

Nitrous acid is a key redox controlling factor, affecting the speciation of neptunium in the reprocessing of used nuclear fuel by solvent extraction. The kinetics of the reduction of neptunium(VI) by nitrous acid in solutions of nitric acid was investigated spectrophotometrically by the method of initial rates. The reaction is of first order with respect to Np(VI) while the order with respect to HNO2 is 1.20 ± 0.04. The reaction rate is almost inversely proportional to the hydrogen ion concentration (reaction order −0.92 ± 0.06), indicating that the reaction proceeds primarily through the reaction of neptunium(VI) with the nitrate anion. The experimental value of the rate constant k for the rate law −d[Np(VI)]/dt = k·[Np(VI)]·[HNO2]1.2/[H+] is of (0.159 ± 0.014) M−0.2 s−1 in I = 4 M and at 20 °C. The activation energy is (−57.3 ± 1.6) kJ/mol, which is in agreement with previous data on this reaction in perchloric acid.

Investigation of the interaction of gold(III)–alkyldiamine complexes with l-histidine and imidazole ligands by 1H and 13C NMR, and UV spectrophotometry

Reactions of Au(III)–alkyldiamine complex with l-histidine and imidazole were carried out and monitored time-dependant by 1H and 13C NMR. Kinetics for the [Au( en)Cl 2] + reaction with l-histidine was determined by initial rate method at constant pH and 25 °C using UV-Vis absorption technique, and found to be first order with respect to each component, with a pseudo second order rate constant of 39 ± 3 M −1 s −1. Reaction rates of l-histidine and imidazole reactions with the [Au( en)Cl 2] + complex was found to be strongly dependant on pD. The pD also has profound effect on the stability of the complex. It was observed that concurrent redox reactions also take place in solution in which Au(III) is reduced to metallic Au(0), while l-histidine and imidazole are oxidized to oxy and hydroxyl products. The optimization of the structure of [(His)Au( en)] 3+ complex was carried out by gaussian03 at the RB3LYP level that showed a distorted square pyramid with the histidine carboxyl group at the pyramid top.

Chromo-chemodosimetric detection for Fe2+ by Fenton reagent-induced chromophore-decolorizing of halogenated phenolsulfonphthalein derivatives

A commercially-available sulfonphthalein derivative was demonstrated to be a chemodosimeter for Fe2+ and its sensing behavior was further investigated by UV-vis spectroscopy in aqueous media under the optimum conditions. In the presence of chlorophenol red (CPR) and H2O2, the absorption maximum at 435 nm decreased upon addition of Fe2+, resulting in a significant color change of the CPR solution from yellow to colorless. The chemosensor system did not show significant responses to a series of other metal ions including Al3+, Zn2+, Cd2+, Hg2+, Mn2+, Co2+, Fe3+, Ni2+, Cu2+, La3+, Ce4+, Th4+, Pd2+, Pb2+, Sb3+, Cr3+, Au3+, Ag+, Nd3+, Sm3+, alkali and alkaline earth metal cations, allowing for highly selective naked-eye detection of Fe2+. Quantitative analysis was carried out kinetically for practicable the Fe2+ assay when either fixed time method or the initial rate method was applied. When the detecting time was set, the decrease of absorbance signal was linear with Fe2+ concentration in the range of 0 to 7.50 × 10−5 mol L−1 and the regression equation was ΔA = 0.00759 + 0.00593CFe with a correlation coefficient r = 0.9953. The chemodosimetric system has employed an irreversible Fenton reagent-promoted oxidation of the CPR free chromophore and the hydroxyl radicals were generated in the presence of both Fe2+ and hydrogen peroxide. The mechanistic interpretation of the signaling process was partially confirmed by the radical scavenging experiment and the FT-IR analysis of the intermediates formed at different reaction periods.

Kinetic Spectrophotometric Determination of N-Acetyl-L-cysteine Based on a Coupled Redox-Complexation Reaction

A novel simple kinetic spectrophotometric method for the determination of N-acetyl-L-cysteine (NAC) has been developed and validated. The proposed method is based on a coupled redox-complexation reaction, the first step of which is the reduction of Fe(3+) by NAC; the second one includes the complexation of Fe(2+), resulting from the preceding redox reaction, with 2,4,6-trypyridyl-s-triazine (TPTZ). The stable Fe(TPTZ)(2)(2+) complex exhibits an absorption maximum at lambda = 593 nm.The initial rate and fixed-time (at 5 min) methods were utilized for constructing calibration graphs. The graphs were linear in concentration ranges from 4.0 x 10(-6) to 1.0 x 10(-4) mol L(-1) for the initial rate method and 1.0 x 10(-6) to 1.0 x 10(-4) mol L(-1) for the fixed-time method, with detection limits of 1.0 x 10(-6) and 1.7 x 10(-7) mol L(-1), respectively. The proposed methods were successfully applied for the determination of NAC in its commercial pharmaceutical formulations.

Hypothesis testing for the validation of the kinetic spectrophotometric methods for the determination of lansoprazole in bulk and drug formulations via Fe(iii) and Zn(ii) chelates

Point and interval hypothesis tests performed to validate two simple and economical, kinetic spectrophotometric methods for the assay of lansoprazole are described. The methods are based on the formation of chelate complex of the drug with Fe(III) and Zn(II). The reaction is followed spectrophotometrically by measuring the rate of change of absorbance of coloured chelates of the drug with Fe(III) and Zn(II) at 445 and 510 nm, respectively. The stoichiometric ratio of lansoprazole to Fe(III) and Zn(II) complexes were found to be 1:1 and 2:1, respectively. The initial-rate and fixed-time methods are adopted for determination of drug concentrations. The calibration graphs are linear in the range 50-200 µg ml⁻¹ (initial-rate method), 20-180 µg ml⁻¹ (fixed-time method) for lansoprazole-Fe(III) complex and 120-300 (initial-rate method), and 90-210 µg ml⁻¹ (fixed-time method) for lansoprazole-Zn(II) complex. The inter-day and intra-day precision data showed good accuracy and precision of the proposed procedure for analysis of lansoprazole. The point and interval hypothesis tests indicate that the proposed procedures are not biased.

Kinetics of the Mono-esterification Between Terephthalic Acid and 1,4-Butanediol

The chemical kinetics of the monoesterification between terephthalic acid (TPA) and 1,4-butanediol (BDO) catalyzed by a metallo-organic compound was studied using the initial rate method. The experiments were carried out in the temperature range of 463-483 K, and butylhydroxyoxo-stannane (BuSnOOH) and tetrabutyl titanate [Ti(OBu) 4] were used as catalyst respectively. The initial rates of the reaction catalyzed by BuSnOOH or Ti(OBu) 4 were measured at a series of initial concentrations of BDO (or TPA) with the concentration of TPA (or BDO) kept constant. The reaction orders of reagents were determined by the initial rate method. The results indicate that the reaction order for TPA is related with the species of catalyst and it is 2 and 0.7 for BuSnOOH and Ti(OBu) 4 respectively. However, the order for BDO is the same 0.9 for the two catalysts. Furthermore, the effects of temperature and catalyst concentration are investigated, and the activation energies and the reaction rate constants for the two catalysts were determined.

Mechanistic Investigation of the Dipolar [2+2] Cycloaddition–Cycloreversion Reaction between 4‐(N,N‐Dimethylamino)phenylacetylene and Arylated 1,1‐Dicyanovinyl Derivatives To Form Intramolecular Charge‐Transfer Chromophores

The kinetics and mechanism of the formal [2+2] cycloaddition-cycloreversion reaction between 4-(N,N-dimethylamino)phenylacetylene (1) and para-substituted benzylidenemalononitriles 2 b-2 l to form 2-donor-substituted 1,1-dicyanobuta-1,3-dienes 3 b-3 l via the postulated dicyanocyclobutene intermediates 4 b-4 l have been studied experimentally by the method of initial rates and computationally at the unrestricted B3LYP/6-31G(d) level. The transformations were found to follow bimolecular, second-order kinetics, with DeltaH(exp)(not equal)=13-18 kcal mol-1, DeltaS(exp)(not equal) approximately -30 cal K-1 mol-1, and DeltaG(exp)(not equal)=22-27 kcal mol-1. These experimental activation parameters for the rate-determining cycloaddition step are close to the computational values. The rate constants show a good linear free energy relationship (rho=2.0) with the electronic character of the para-substituents on the benzylidene moiety in dimethylformamide (DMF), which is indicative of a dipolar mechanism. Analysis of the computed structures and their corresponding solvation energies in acetonitrile suggests that the rate-determining attack of the nucleophilic, terminal alkyne carbon onto the dicyanovinyl electrophile generates a transient zwitterion intermediate with the negative charge developing as a stabilized malononitrile carbanion. The computational analysis predicted that the cycloreversion of the postulated dicyanocyclobutene intermediate would become rate-determining for 1,1-dicyanoethene (2 m) as the electrophile. The dicyanocyclobutene 4 m could indeed be isolated as the key intermediate from the reaction between alkyne 1 and 2 m and characterized by X-ray analysis. Facile first-order cycloreversion occurred upon further heating, yielding as the sole product the 1,1-dicyanobuta-1,3-diene 3 m.

Thermokinetics: Iodide-Catalyzed Decomposition Kinetics of Hydrogen Perioxide. An Initial-Rate Approach

A temperature-based determination of the kinetics of the H2O2 decomposition using the method of initial rates is described. The reagents (total volume 5 mL) are added to a microcalorimeter and the temperature–time data are collected using a temperature sensor and a datalogger. The temperature–time plots are linear for a considerable length of time allowing for a straightforward and accurate determination of the initial rate, dT/dt. Changing from dT/dt to an initial rate in terms of H2O2 concentration (–d[H2O2]/2dt), requires the determination of the enthalpy of the reaction as well as the heat capacity of the microcalorimeter. In doing so, this lab combines thermochemistry and kinetics. The reaction is first order with respect to the catalyst, [I–], and first order with respect to [H2O2]. The average rate constant reported by students is 0.0108 ± 0.0003 L mol–1 s–1 at ~20 °C.

Oxygen influence on amino acid oxidative deamination catalyzed by different amino acid oxidases

Amino acid oxidases catalyze oxidative deamination of a wide range of amino acids to their corresponding  -keto acids. In this work two D-amino acid oxidases: from porcine kidney and Arthrobacter protophormiae were compared in their action in the reaction of D-methionine oxidative deamination. Special attention has been paid to the oxygen influence on enzyme activity. Kinetics of the reaction was determined by the initial reaction rate method by the standard peroxidase-o-dianisidine enzyme assay. The oxygen impact on the initial reaction rate was measured by following the oxygen consumption during the reaction at different initial oxygen concentration. Kinetic parameters were estimated from the experimental results by using the non-linear regression analysis implemented in the package program SCIENTIST. It was found that both enzymes have similar affinities towards D-methionine as well as oxygen ( (porcine kidney)=0.13 mM, (A. protophormiae)=0.22 mM). Both enzymes are inhibited by 2-oxo-4-methylthiobutyric acid, and the inhibition constant is lower in the case of porcine kidney enzyme which indicates higher inhibition. Oxygen volume transfer coefficient (kLa) has been determined at different air flow-rates using integral. Mathematical model of the process that consists of kinetic and mass balance equations has been developed in the batch reactor. The experiments without and with continuous oxygen (air) supply were carried out to validate the mathematical model. The reaction solution was initially saturated with air to achieve the maximum oxygen solubility at the experimental conditions. Considering that oxygen is one of the reactants spent in the reaction, the reaction rate in the initial part of the experiments is faster if air is supplied to the reactor. In the case of porcine kidney oxidase the reaction was very slow without the air supply. 100 % D-methionine conversion was achieved after 12 hours. Another two experiments were carried out at the continuous air supply (flow-rates 5 and 10 L/h). The reaction went faster in the initial part of both experiments ; however enzyme deactivation occurred and prevented the complete substrate conversion. In the case of oxidase from A. protophormiae experiments without and with the air supply (flow-rate 10 L/h) were carried. In both cases 100 % D-methionine conversion could be achieved. This enzyme was more tolerant to oxygen since enzyme deactivation constant (kd = 7.9  10-5 min-1) was found to be several orders of magnitude lower than the ones estimated for D-AAO from porcine kidney (kd, 5L/h= 0.0108 and kd, 10L/h=0.0198 min-1).

Effect of particle size on the rate of enzymatic hydrolysis of cellulose

The effect of particle size on enzymatic hydrolysis of cellulose has been investigated. The average size of microcrystalline cotton cellulose has been reduced to submicron scale by using a media mill. The milled products were further subjected to hydrolysis using cellulase. High cellulose concentration (7%) appeared to retard the size reduction and resulted in greater particles and smaller specific surface areas than those at low concentration (3%) with the same milling time. Initial rate method was employed to explore the rate of enzymatic hydrolysis of cellulose. The production rate of cellobiose was increased at least 5-folds due to the size reduction. The yield of glucose was also significantly increased depending upon the ratio of enzyme to substrate. A high glucose yield (60%) was obtained in 10-h hydrolysis when the average particle size was in submicron scale.

Beneficial Effect of Solubility Enhancers on Protein Crystal Nucleation and Growth

Crystallizing solutions of proteins often contain various nonelectrolyte additives that arise from the purification process of proteins or from the reagents employed in the screening kits. Currently, limited knowledge exists about the influence of these additives on the mechanisms underlying the crystallization process, in particular on the nucleation stage of crystals. To address this need, we studied crystallization of two proteins, D-xylose isomerase and chicken egg-white lysozyme, in small batches and in the presence of two solubility-enhancing additives, acetonitrile and glycerol. We have also measured the nucleation rates of crystals of these proteins in the presence and in the absence of acetonitrile using the method of initial rates. With the addition of the solubility enhancers, both proteins exhibited an increase in crystal nucleation at any given supersaturation. Solubility enhancing additives appear to lower the energy barrier to nucleation by influencing the strength of attraction between the protein molecules. We have characterized the quality of D-xylose isomerase crystals by determining the crystal mosaicity, which showed considerable improvement for crystals grown in the presence of additives. When compared to the crystals of chicken egg-white lysozyme, D-xylose isomerase crystals required higher supersaturations to nucleate. We attribute this result to the large size of the D-xylose isomerase molecule, which influences the energy barrier to nucleation by increasing the surface area of the critical nucleus. Contrary to the common expectation that reagents that solubilize the protein may hinder the crystallization process, our results suggest that solubility enhancers, in fact, can have a beneficial effect on the nucleation and growth of crystals. These findings are of importance in formulating successful strategies toward crystallizing new proteins.

Effects of Concentration of Some Lanthanide(III) Complexes of 1,7‐Bis(carboxymethyl)‐1,4,7,10‐tetraazacyclododecane on Bis(p‐nitrophenyl)phosphate Hydrolysis

AbstractA detailed study of the effects of the concentration of some lanthanide(III) complexes [LnDO2A+; DO2A = 1,7‐bis(carboxymethyl)‐1,4,7,10‐tetraazacyclododecane] on the hydrolysis of the phosphodiester bond of the compound BNPP [sodium bis(4‐nitrophenyl)phosphate] is reported at 25 °C and pH 7.90 (Ln = Eu), 9.35 (Ln = Eu), and 9.90 (Ln = Eu, Er and Yb). The reaction is found to be first order with respect to BNPP concentration at pH 7.90 and 9.35 and to increase to 1.78 ± 0.09, 1.64 ± 0.07, and 1.63 ± 0.09 with respect to [EuDO2A+] concentration at pH 7.90, 9.35, and 9.90, respectively, thereby indicating that dinuclear species are involved in the reactions. Similar observations were found for the other two LnDO2A+ complexes at pH 9.90 [1.63 ± 0.11 (Er) and 1.49 ± 0.09 (Yb)]. The kobs data obtained by the initial rate method could be fitted to a monomer‐dimer reaction model for all LnDO2A+ complexes at pH 7.90, 9.35, and 9.90 in the [LnDO2A+] concentration range 1.0–20.0 mM. The dinuclear species, namely the mono‐hydroxo‐bridged complexes [Ln2(DO2A)2(μ‐OH)(OH)(H2O)n = 1–3] and the di‐hydroxo‐bridged complexes [Ln2(DO2A)2(μ‐OH)2(H2O)n = 0–2] are found to be more reactive, with reactivities in the order Eu > Yb > Er. The overall formation constants for [Ln2(DO2A)2(μ‐OH)2(H2O)n]‐BNPP are around 104 M–1. The EuDO2A+‐promoted BNPP hydrolysis rates are similar to, or up to two orders of magnitude faster than, most of those reported for other lanthanide and transition‐metal complexes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Determination of doxycycline in pharmaceuticals based on its degradation by Cu(II)/H2O2 reagent in aqueous solution

The reaction between doxycycline, hydrogen peroxide and Cu(II) was investigated spectrophotometrically in aqueous solutions. The absorption spectra show that the degradation of antibiotic drug occurs in weak alkaline aqueous solutions. The kinetics of the reaction was studied by applying the initial-rate method and the relative rate constants were calculated at different temperatures. The kinetic-spectrophotometric method for the determination of doxycycline based on the kinetics of pseudo-first order reaction at 20°C is proposed. The effects of several molecules and ions usually present in pharmaceutical formulations were studied in order to assess their interference. The calibration graph was applied to the determination of doxycycline in capsule dosage form. The relative standard deviation was no greater than 3.80%. The results were compared to those obtained by the official HPLC method.

Electroless Pd and Ag deposition kinetics of the composite Pd and Pd/Ag membranes synthesized from agitated plating baths

The atomic absorption spectroscopy (AAS) has been successfully utilized for the measurement of the Pd and Ag ion concentrations in the plating baths and to elucidate the effects of temperature, initial metal ion and reducing agent concentrations and agitation on the electroless plating kinetics of Pd and Ag metals. The initial metal ion concentrations for Pd and Ag were varied over a range of 8.2–24.5 mM and 3.1–12.5 mM, respectively. The plating reactions were conducted in a constant temperature electroless plating bath over a temperature range of 20–60 °C and an initial hydrazine concentration range of 1.8–5.4 mM. It was found that the electroless plating of both Pd and Ag were strongly affected by the external mass transfer in the absence of bath agitation. The external mass transfer limitations for both Pd and Ag deposition have been minimized at or above an agitation rate of 400 rpm, resulting in a maximum conversion of the plating reaction at 60 °C and dramatically shortened plating times with the added advantage of uniform deposition morphology. The derivation of the differential rate laws and the estimation of the reaction orders and the activation energies for the electroless Pd and Ag kinetics were conducted via non-linear regression analysis based on the method of initial rates. For a constant-volume batch reactor, the integrated rate law was solved to calculate the conversion and the reactant concentrations as a function of plating time. The model fits were in good agreement with the experimental data. Furthermore, the bath agitation and the plating conditions used in the kinetics study were adopted for the synthesis of 16–20 μm thick composite Pd/Ag membranes (10–12 wt% Ag) and a pure-Pd membrane with a hydrogen selective dense Pd layer as thin as 4.7 μm. While hydrogen permeance of the Pd/Ag membranes A and B at 450 °C were 28 and 32 m 3/m 2-h-atm 0.5, the H 2 permeance for the 4.7 μm thick pure-Pd membrane at 400 °C was as high as 63 m 3/m 2-h-atm 0.5 . The long-term permeance testing of all the membranes synthesized from agitated plating baths resulted in a relatively slow leak growth due primarily to the improved morphology obtained via the bath agitation and modified plating conditions.

The regulation and catalytic mechanism of the NADP-malic enzyme from tobacco leaves

The non-photosynthetic NADP-malic enzyme EC 1.1.1.40 (NADP-ME), which catalyzes the oxidative decarboxylation of L-malate and NADP+ to produce pyruvate and NADPH, respectively, and which could be involved in plant defense responses, was isolated from Nicotiana tabacum L. leaves. The mechanism of the enzyme reaction was studied by the initial rate method and was found to be an ordered sequential one. Regulation possibilities of purified cytosolic NADP-ME by cell metabolites were tested. Intermediates of the citric acid cycle (?-ketoglutarate, succinate, fumarate), metabolites of glycolysis (pyruvate, phosphoenolpyruvate, glucose-6-phosphate), compounds connected with lipogenesis (coenzyme A, acetyl-CoA, palmitoyl-CoA) and some amino acids (glutamate, glutamine, aspartate) did not significantly affect the NADP-ME activity from tobacco leaves. In contrast, macroergic compounds (GTP, ATP and ADP) were strong inhibitors of NADP-ME; the type of inhibition and the inhibition constants were determined in the presence of the most effective cofactors (Mn2+ or Mg2+), required by NADP-ME. Predominantly non-competitive type of inhibitions of NADP-ME with respect to NADP+ and mixed type to L-malate were found.

Estudio cinético de la descomposición catalizada de peróxido de hidrógeno sobre carbón activado

The kinetic study of decomposition of hydrogen peroxide catalyzed by activated carbon was carried out. The effect of concentrations of reactants and temperature were experimentally studied. Kinetic data were evaluated using differential method of initial rates of reaction. When a typical kinetic law for reactions in homogeneous phase is used, first order of reaction is obtained for hydrogen peroxide and activated carbon, and activation energy of 27 kJ mol-1 for the reaction was estimated. Experimentally was observed that surface of activated carbon is chemically modified during decomposition of hydrogen peroxide, based on this result a scheme of reaction was proposed and evaluated. Experimental data fits very well to a Langmuir- Hinshelwood kinetic model and activation energy of 40 kJ mol-1 was estimated for reaction in heterogeneous phase.

The measurement of serum cholinesterase activities by an integration strategy with expanded linear ranges and negligible substrate-activation

Objectives To measure serum cholinesterase (SCHE) with an integration strategy. Design and methods At 54.0 μmol/L butyrylthiolcholine, SCHE initial rates were calculated with 50.0 μmol/L butyrylthiolcholine and maximal rates via an improved integrated method if substrate consumptions within 5.0 min were over 60%, or were determined by the classical initial rate method. Results The linear range was from 16 to 1560 nkat/L, and SCHE in clinic sera showed negligible substrate-activation. Conclusion This strategy was effective.

Experimental kinetics and dynamics of hydrogen production on glucose by hydrogen forming bacteria (HFB) culture

The kinetic study was performed using a modified “initial rate-method” and the dynamic ones by the relaxation time methodology. The approach was tested on glucose as sole carbon source while the hydrogen forming bacteria HFB were obtained by acid treatment of anaerobic sludge. A large spectrum of substrate concentration from 5 g/l to 90 g/l was experimentally tested. During the test biogas evolution, gas composition, glucose concentration as well as pH and Red-Ox Potential (ROP) were monitored. At the end of the tests ethanol and VFA were measured to evaluate a reference molar H 2 yield ( Y*). The biogas composition ranged in (40–60%) for H 2 and rest CO 2, no CH 4 was observed. A first order kinetic equation for glucose with a kinetic constant of 0.0041 h −1 and an inhibited kinetic equation for biogas evolution with a maximum production rate of 100 ml/l h were set-up. The dynamic study evidences the strong role of the pH in the regulation of activity of the Ferrodoxin and Hydrogenase pools. Lastly a test with a bioreactor of 2 l with pH adjustments validated the dynamics of the system showing an increase of 2.8 times of efficiency of glucose conversion into H 2 compared with tests without pH adjustments and agitation.