Cresol Formation Research Articles

Catalytic conversion of biomass pyrolysis volatiles over composite catalysts of activated carbon and HY zeolite

Bio-oil has complex compositions and high oxygen content, which restricts its high-value utilization. Commercial activated carbon (AC) and HY zeolite were used as composite catalysts to study their effect on pyrolysis volatiles from rice straw and poplar sawdust by changing the mixing modes of two catalysts. The results showed that the loading modes of AC and HY zeolite obviously affected the products distribution and bio-oil components. The lowest yield of bio-oil was obtained when HY zeolite and AC were mechanically mixed at a mass ratio of 1:1 (YACM). But the loading mode of YACM was beneficial to the deoxidation and aromatic hydrocarbon generation. Under the mode of YACM, the aromatics content in rice straw and poplar sawdust bio-oil can be increased from 13.8% and 8.0% without catalyst to 56.4% and 53.1%, respectively. However, the layered loading with upper HY zeolite and lower AC (YTACL) was favorable for formation of phenolic compounds. The selectivity to monocyclic and bicyclic aromatic hydrocarbons followed the order of YTACL > ACTYL > YACM, and YACM > ACTYL > YTACL, respectively. Compared with HY zeolite, AC catalyst possessed smaller pore size and fewer acidity, and the active sites of AC were conducive to rearrangement of furan compounds to generate cyclopentanone, 2-cyclopentenone and methyl-cyclopentenone, and further rearrangement to form phenol. Therefore, the loading mode of YTACL exhibited a promotion effect on the formation of phenol, cresol, toluene, ethylbenzene and p-xylene. The strong acidic sites of HY zeolite were favorable for the aromatization, so the loading mode of ACTYL had good selectivity to the formation of naphthalene, methylnaphthalene, anthracene and pyrene. This work will provide a guide for products regulation from biomass pyrolysis and enrich aromatics and phenols in bio-oil.

Low temperature oxidation of toluene in an n-heptane/toluene mixture

As an important component of transportation fuels, toluene has little reactivity in the low temperature regime. However, the low temperature reactivity of toluene may be enhanced by the reaction of other reactive components (e.g., n-heptane) in fuel mixtures. This work examines low temperature oxidation of toluene in jet stirred reactor oxidation of an n-heptane/toluene mixture (1:1 in mole, 500–800 K, ϕ=0.5, τ=2.0 s, p = 1 bar). Two measurement techniques, time of flight molecular beam mass spectrometry using synchrotron vacuum ultraviolet radiation as the photon ionization source and gas chromatography mass spectrometry, were applied to identify and measure 32 species, including four polycyclic aromatic hydrocarbons (PAH) and oxygenated PAH (OPAH). Numerical simulations using the latest kinetic model from Lawrence Livermore National Laboratory predicted the mole fractions of fuel molecules and small intermediates well, but under-predicted the mole fractions of oxygenated aromatics (phenol, benzyl alcohol, and cresol). The identification of benzyl peroxide–an important intermediate–supported the proposed formation pathways for the identified aromatics. Model analysis highlighted the influence of H-atom abstraction, OH/H radical ipso substitution, and OH addition reactions of toluene on the formation of phenol, benzyl alcohol, and cresol, which may further grow to OPAH molecules by the addition of benzyl radical from H-atom abstraction of toluene.

Competing pathways of cresol formation in toluene photooxidation: OH-toluene adducts react with NO2 or with O2?

Methyl-hydroxy-cyclohexadienyl radicals (OTAs) are the key products of the photooxidation of toluene, with implications for the fate of toluene. Hence, we investigated the photooxidation mechanisms and kinetics of three main OTAs (o-OTA, m-OTA, and p-OTA) with NO2 using quantum chemical calculations as well as the fate of OTAs under the different concentration ratios of NO2 and O2. The mechanism results show that the pathway of H-abstraction by NO2 to anti-HONO (anti-H-abstraction) is more favorable than the syn-H-abstraction pathway, because the strong interaction between OTAs and NO2 is formed in the transition states of the anti-H-abstraction pathways. The branching ratios of the anti-H-abstraction pathways are more than 99% in the temperature range of 216−298 K. The total rate constant of the OTA-NO2 reaction is 9.9 × 10−12 cm3/(molecule∙sec) at 298 K, which is contributed about 90% by o-OTA + NO2, and the main products are o-cresol and anti-HONO. The half-lives of the OTA-NO2 reaction in some polluted areas of China are 35 times longer than those of the OTA-O2 reaction. In the atmosphere, the NO2- and O2- initiated reactions of OTAs have the same ability to form cresols as [NO2] is up to 142.1 ppmV, which is impossible to achieve. It implies that under the experimental condition, the [NO2]/[O2] should be controlled to be less than 7.8 × 10−5 to simulate real atmospheric oxidation of toluene. Our results reveal that for the photooxidation of toluene, the yield of cresol is not affected by the concentration of NO2 under the atmospheric environment.

Fast pyrolysis of guaiacol to simple phenols: Experiments, theory and kinetic model

This study is focused on both experimental and theoretical analysis of fast pyrolysis of guaiacol, a major pyrolysate and a model monomeric compound of lignin. Fast pyrolysis experiments were performed in an analytical pyrolyzer coupled with gas chromatograph/mass spectrometer in the temperature range of 450–650 °C. Thermodynamics and kinetics of 19 elementary reactions of 17 species were investigated using quantum chemical density functional theory calculations. Reaction pathways for the formation of four major phenols, viz. phenol, catechol, o-hydroxybenzaldehyde and o-cresol, were proposed. The homolytic cleavage of OCH3 bond, with low bond dissociation energy of 57.7 kcal/mol, is shown to be the primary reaction for the generation of free radicals. The generation of o-hydroxyphenyl radical is found to be vital for the formation of phenol and cresol, while o-hydroxybenzyloxy radical is the key intermediate for the formation of o-hydroxybenzaldehyde. Multiple pathways for the formation of catechol were evaluated. A kinetic model was developed using the elementary reactions and their Arrhenius rate parameters. The concentration of the major products at different temperatures obtained from the model reasonably matched the trends in product yields from the experiments.

Investigation on pyrolysis mechanism of guaiacol as lignin model compound at atmospheric pressure

Understanding the pyrolysis mechanism of lignin is of great importance for improvement of thermochemical conversion processes and upgrading of biofuels. In this work, the pyrolysis of lignin model compound, guaiacol, at atmospheric pressure has been studied in a flow reactor by synchrotron vacuum ultraviolet photoionization mass spectrometry. Over 50 species were detected and identified in guaiacol pyrolysis, including alkanes, alkenes, cyclic alkenes, dienes, alkynes and aromatics. Major pathways proposed, including homolytic cleavage of O-CH3 bond, isomerization, dehydrogenation and hydrogenation, were evaluated using quantum chemical calculations. In the proposed pathways, homolytic cleavage of O-CH3 bond is regarded as an important route for the formation of catechol. H-atom and CH3-radical assisted demethoxylation mechanisms were proposed to interpret the formation of phenol and cresol, respectively. Furthermore, an energetically advantageous route including intramolecular H-immigration, ring-opening and decarbonylation was proposed to account for the formation of C4 products. A series of aromatic products were detected in this work, which is helpful to understand the coking mechanism during pyrolysis of lignin.

A study of the hydrodeoxygenation of anisole over Re-MoOx/TiO2 catalyst

A well-characterized Re-MoOx/TiO2 catalyst was used to investigate the reaction sequence involved during the hydrodeoxygenation of anisole in a batch reactor by varying the initial anisole concentration in the reactant mixture (0.182–0.382molL−1 corresponding to 2.6–5.4wt.%), the reaction temperature (250–325°C) and hydrogen pressure (30–60bar). The effects of these process variables on product selectivity, calculated at 10% anisole conversion, and reaction rate, estimated from the initial slope of anisole conversion vs. time, were discussed. The initial reaction rate was observed to increase to a maximum at anisole concentration of 0.282molL−1 and then decrease at higher concentrations. Mathematical modeling of the proposed reaction network revealed that the decreased activity at higher anisole concentration is related to diminished ability to cleave CO bonds on phenol and cresols, probably due to increased surface coverage by the reactant on the oxophilic sites on the catalyst which limits access to surface reactive hydrogen for transformation. In regards to the influence of reaction temperature, high temperature favors the formation of cresols at the expense of benzene which was confirmed by the estimated apparent activation energy of the different pathways. On the other hand, the observed strong dependence of benzene/phenol ratio on H2 pressure is attributed to increased availability of surface reactive hydrogen surface to aid in oxygen removal. Results from this study and the literature indicates that CO bond breaking is preceded by either protonation of oxygen on anisole or by partial hydrogenation of the aromatic ring to lower the CO scission barrier. Analysis of the conversion of intermediate compounds confirmed the reaction sequence and preferences during anisole HDO on Re-MoOx/TiO2 catalyst.

Correlation between coal structure and release of the two organic compounds during pyrolysis

Abstracts A considerable amount of organic compounds could be released during coal utilization processes, and these compounds could have a significant detrimental effect on the environment and human health if freely discharged. In this study, we investigated the yields of two organic compounds (PAHs and phenols) released during the pyrolysis of coals with different ranks. And then, the formation mechanisms of PAHs and phenols are discussed by means of comparisons the correlation between release principles and coal structure. The results showed that the yields of PAHs and phenols depended to a large extent on coal structure. PAHs are formed not only by thermal breakdown of coal structure, but also by the combination of different low molecule weight compounds with each other. Monohydric phenolic carbon and aromatic ether carbon were likely to be the precursor structure of phenols. The formation of phenol, cresol and xylenol are closely related to the types of free radical (like H or CH 3 ) and the chemical structure of oxygenated aromatic carbon in coal during pyrolysis.

Methanogenic toluene metabolism: community structure and intermediates

Toluene is a model compound used to study the anaerobic biotransformation of aromatic hydrocarbons. Reports indicate that toluene is transformed via fumarate addition to form benzylsuccinate or by unknown mechanisms to form hydroxylated intermediates under methanogenic conditions. We investigated the mechanism(s) of syntrophic toluene metabolism by a newly described methanogenic enrichment from a gas condensate-contaminated aquifer. Pyrosequencing of 16S rDNA revealed that the culture was comprised mainly of Clostridiales. The predominant methanogens affiliated with the Methanomicrobiales. Methane production from toluene ranged from 72% to 79% of that stoichiometrically predicted. Isotope studies using (13)C(7) toluene showed that benzylsuccinate and benzoate transiently accumulated revealing that members of this consortium can catalyse fumarate addition and subsequent reactions. Detection of a BssA gene fragment in this culture further supported fumarate addition as a mechanism of toluene activation. Transient formation of cresols, benzylalcohol, hydroquinone and methylhydroquinone suggested alternative mechanism(s) for toluene metabolism. However, incubations of the consortium with (18)O-H(2)O showed that the hydroxyl group in these metabolites did not originate from water and abiotic control experiments revealed abiotic formation of hydroxylated species due to reactions of toluene with sulfide and oxygen. Our results suggest that toluene is activated by fumarate addition, presumably by the dominant Clostridiales.

Formation of secondary aerosols over Europe: comparison of two gas-phase chemical mechanisms

Abstract. The impact of two recent gas-phase chemical kinetic mechanisms (CB05 and RACM2) on the formation of secondary inorganic and organic aerosols is compared for simulations of PM2.5 over Europe between 15 July and 15 August 2001. The host chemistry transport model is Polair3D of the Polyphemus air-quality platform. Particulate matter is modeled with a sectional aerosol model (SIREAM), which is coupled to the thermodynamic model ISORROPIA for inorganic species and to a module (MAEC) that treats both hydrophobic and hydrophilic species for secondary organic aerosol (SOA). Modifications are made to the gas-phase chemical mechanisms to handle the formation of SOA. In order to isolate the effect of the original chemical mechanisms on PM formation, the addition of reactions and chemical species needed for SOA formation was harmonized to the extent possible between the two gas-phase chemical mechanisms. Model performance is satisfactory with both mechanisms for speciated PM2.5. The monthly-mean difference of the concentration of PM2.5 is less than 1 μg m−3 (6%) over the entire domain. Secondary chemical components of PM2.5 include sulfate, nitrate, ammonium and organic aerosols, and the chemical composition of PM2.5 is not significantly different between the two mechanisms. Monthly-mean concentrations of inorganic aerosol are higher with RACM2 than with CB05 (+16% for sulfate, +11% for nitrate, and +10% for ammonium), whereas the concentrations of organic aerosols are slightly higher with CB05 than with RACM2 (+22% for anthropogenic SOA and +1% for biogenic SOA). Differences in the inorganic and organic aerosols result primarily from differences in oxidant concentrations (OH, O3 and NO3). Nitrate formation tends to be HNO3-limited over land and differences in the concentrations of nitrate are due to differences in concentration of HNO3. Differences in aerosols formed from aromatic SVOC are due to different aromatic oxidation between CB05 and RACM2. The aromatic oxidation in CB05 leads to more cresol formation, which then leads to more SOA. Differences in the aromatic aerosols would be significantly reduced with the recent CB05-TU mechanism for toluene oxidation. Differences in the biogenic aerosols are due to different oxidant concentrations (monoterpenes) and different particulate organic mass concentrations affecting the gas-particle partitioning of SOA (isoprene). These results show that the formulation of a gas-phase chemical kinetic mechanism for ozone can have significant direct (e.g., cresol formation) and indirect (e.g., oxidant levels) effects on PM formation. Furthermore, the incorporation of SOA into an existing gas-phase chemical kinetic mechanism requires the addition of reactions and product species, which should be conducted carefully to preserve the original mechanism design and reflect current knowledge of SOA formation processes (e.g., NOx dependence of some SOA yields). The development of chemical kinetic mechanisms, which offer sufficient detail for both oxidant and SOA formation is recommended.

Extent of H-atom abstraction from OH + p-cymene and upper limits to the formation of cresols from OH + m-xylene and OH + p-cymene

Aromatic hydrocarbons are important constituents of vehicle exhaust and of non-methane volatile organic compounds in ambient air in urban areas. It has recently been proposed that dealkylation is a significant pathway for the OH radical-initiated reactions, leading to the formation of phenolic compounds and/or oxepins (Noda, J., Volkamer, R., Molina, M.J., 2009. Dealkylation of alkylbenzenes: a significant pathway in the toluene, o-, m-, and p-xylene + OH reaction. Journal of Physical Chemistry A 113, 9658–9666.). We have investigated the formation of cresols from the reactions of OH radicals with m-xylene and p-cymene, and obtain upper limits of <1% for formation of each cresol isomer from OH + m-xylene and <2% for formation of each cresol isomer from OH + p-cymene. In addition, we have measured the formation yield of 4-methylacetophenone (the major product formed subsequent to H-atom abstraction from the CH(CH 3) 2 group) in the OH + p-cymene reaction to be 14.8 ± 3.2%, and estimate that H-atom abstraction from the CH 3 and CH(CH 3) 2 groups in p-cymene accounts for 20 ± 4% of the overall OH radical reaction. We also used a relative rate technique to measure the rate constant for the reaction of OH radicals with 4-methylacetophenone to be (4.50 ± 0.43) × 10 −12 cm 3 molecule −1 s −1 at 297 ± 2 K.

Selective synthesis of p-cresol by methylation of phenol

Abstract The selective synthesis of p -cresol by gas-phase alkylation of phenol with methanol was studied on SiO 2 –Al 2 O 3 and zeolites HBEA, HZSM5 and HMCM22. Cresols were formed from phenol alkylation of methanol via two parallel pathways: the direct C -alkylation of phenol and the conversion of anisole intermediate obtained by O -alkylation of phenol. Methylation of o - and p -cresol led to the formation of 2,6- and 2,4-xylenols while anisole produced methylanisoles either by alkylation with methanol or by disproportionation. Regarding the cresol isomers distribution, p - and o -cresol were the major products on all the samples while m -cresol formation remained always lower than 6%. SiO 2 –Al 2 O 3 , HBEA and HZSM5 exhibited similar initial p -cresol: o -cresol ratios, between 0.6 and 0.8. In contrast, p -cresol was the predominant product on HMCM22 because the narrow sinusoidal 10-membered ring channels of this zeolite were particularly suitable for improving by shape selectivity the formation of p -cresol. Thus, we report here that p -cresol yields of 55% and p -cresol: o- cresol ratios of 4 are obtained on HMCM22 by gas-phase alkylation of phenol with methanol at 473 K, atmospheric pressure and contact time of 350 g h/mol phenol.

OH-Initiated Oxidation of Toluene. 3. Low-Energy Routes to Cresol and Oxoheptadienal

The toluene-OH-O2 system implicated in the atmospheric degradation of toluene is studied further using quantum chemistry methods. Two new reaction mechanisms are explored as alternatives to the previously proposed mechanism. While the previous mechanism involves surmounting a 170 kJ/mol barrier, the new equivalent cresol formation route has a barrier above the asymptotic state calculated to be 12 kJ/mol at the B3LYP/6-311G(2df,2pd) level. The new oxoheptadienal formation route occurs via two successive reactions with OH, with the highest barrier lying 200 kJ/mol below the energy of the reactants. Neither of the newly proposed reaction mechanisms involves forming a toluene oxide intermediate.

Selective Oxidation of Toluene with Hydrogen Peroxide Catalyzed by V-Mo-based Catalyst

Abstract The selective catalytic oxidation of toluene with hydrogen peroxide over V-Mo-based catalysts under mild conditions was studied. The promotion effect of Mo on the catalysts was studied with V/Al2O3 and Mo/Al2O3 as reference samples. The catalysts were characterized by XRD, TPR, and XPS techniques. The results show that the addition of Mo to V/Al2O3 may change the distribution of V species on Al2O3 surface. Over V-Mo/Al2O3 catalyst, highly dispersed amorphous V species facilitates benzaldehyde formation, and crystalline V2O5 species increases the conversion of toluene but decreases the selectivity to benzaldehyde, while AlVMoO7 species favors both the conversion of toluene and the formation of cresols. The yield of benzaldehyde depends remarkably on the surface O/Al and Mo/V atomic ratios, and gets to a maximum value of 13.2% with a selectivity of 79.5% at an O/Al atomic ratio of 3.0 and Mo/V atomic ratio of 0.7.

4-Hydroxyphenylacetate Decarboxylases: Properties of a Novel Subclass of Glycyl Radical Enzyme Systems

The 4-hydroxyphenylacetate decarboxylases from Clostridium difficile and Clostridium scatologenes, which catalyze the formation of p-cresol, form a distinct group of glycyl radical enzymes (GREs). Cresol formation provides metabolic toxicity, which allows an active suppression of other microbes and may provide growth advantages for the producers in highly competitive environments. The GRE decarboxylases are characterized by a small subunit, which is not similar to any protein of known function in the databases, and provides unique properties that have not been observed in other GREs. Both decarboxylases are functional hetero-octamers (beta(4)gamma(4)), which contain iron-sulfur centers in addition to the glycyl radical prosthetic group. The small subunit is responsible for metal binding and is also involved in the regulation of the enzymes' oligomeric state and activity, which are triggered by reversible serine phosphorylation of the glycyl radical subunits. Biochemical data suggest that the iron-sulfur centers of the decarboxylases could be involved in the radical dissipation of previously activated enzymes in the absence of substrate. The cognate activating enzymes differ from their Pfl and Nrd counterparts in that up to two iron-sulfur centers, in addition to the characteristic SAM cluster, were found. Biochemical data suggested that these [4Fe-4S] centers are involved in the electron transfer to the SAM cluster but do not directly participate in the reductive cleavage of SAM. These data imply a tight regulation of p-cresol formation, which is necessary in order to avoid detrimental effects of the toxic product on the producers.

The mechanism of phenol methylation on acid and basic zeolite catalysts

The alkylation of phenol with methanol on HY and CsY/CsOH catalysts was studied in situ under static conditions by 13C NMR spectroscopy. Attention was largely given to the identification of intermediate compounds and mechanisms of anisole, cresol, and xylenol formation. The mechanisms of phenol methylation were found to be different on acid and basic catalysts. The primary process on acid catalysts was the dehydration of methanol to dimethyl ether and methoxy groups. This resulted in the formation of anisole and dimethyl ether, the ratio between which depended on the reagent ratio, which was evidence of similar mechanisms of their formation. Subsequent reactions with phenol gave cresols and anisoles. Cresols formed at higher temperatures both in the direct alkylation of phenol and in the rearrangement of anisole. The main alkylation product on basic catalysts was anisole formed in the interaction of phenolate anions with methanol; no cresol formation was observed. The deactivation of acid catalysts was caused by the formation of condensed aromatic hydrocarbons that blocked zeolite pores. The deactivation of basic catalysts resulted from the condensation of phenol and formaldehyde with the formation of phenol-formaldehyde resins.

Characterisation of a manganese-reducing, toluene-degrading enrichment culture

A bacterial culture (LET-13) was enriched, which uses toluene as sole carbon and energy source, and manganese oxide as terminal electron acceptor. The culture is able to degrade a variety of substituted monoaromatic compounds like p-hydroxy-benzylalcohol, p-hydroxy-benzaldehyde, p-hydroxy-benzoate, phenol and the three isomers of cresol. Benzene, ethylbenzene, all xylenes and naphthalene were not degraded under the experimental conditions used. Based on the results of growth experiments and the detection of intermediates, it is concluded that toluene is degraded via a methyl hydroxylation. A possible side reaction can lead to the formation of cresol. The organisms in the culture look similar; motile rods, which are Gram-negative, oxidase-negative and catalase-negative. The culture was partly identified by phylogenetic analysis of cloned rDNA sequences. The phylogenetic analysis showed that at least two major groups of bacteria are present. One group of bacteria shows 70–80% similarity (based on 16S rRNA gene sequence data) with the Bacteroides-Cytophaga group, and one group consists of members of the β-subclass of the Proteobacteria.

Pyrolysis of kraft lignin in the presence of molten ZnCl2‐KCl mixture

AbstractPyrolysis of kraft lignin was carried out using small reactors with an added ZnCl2‐KCl mixture at three levels of temperature, 500°C, 550°C and 600°C, and three levels of salt‐to‐lignin ratio (SR), 1, 2 and 3. Nineteen kinds of phenolic compound were identified and their quantitative determinations were made by gas chromatography. The yield of gaseous products determined gravimetrically exhibited a strong dependence on the added amount of salt mixture, and its lowest value was obtained at SR of 1. The formation of gaseous products, apparently stemming from decomposition of liquid products and tar, was observed at reaction times longer than 30 min. At SR of 1 and a temperature of 550°C, all phenolic compounds attained their maximum yields almost synchronously at a reaction time of 15 min. Cresol's formation was slightly increased with the amount of added salt mixture. At a temperature of 550°C, cresols and guaiacols decomposed according to a pseudo‐first‐order lumping model, while catechols did not follow the similar model.

Characterisation of a manganese-reducing, toluene-degrading enrichment culture

A bacterial culture (LET-13) was enriched, which uses toluene as sole carbon and energy source, and manganese oxide as terminal electron acceptor. The culture is able to degrade a variety of substituted monoaromatic compounds like p-hydroxy-benzylalcohol, p-hydroxy-benzaldehyde, p-hydroxy-benzoate, phenol and the three isomers of cresol. Benzene, ethylbenzene, all xylenes and naphthalene were not degraded under the experimental conditions used. Based on the results of growth experiments and the detection of intermediates, it is concluded that toluene is degraded via a methyl hydroxylation. A possible side reaction can lead to the formation of cresol. The organisms in the culture look similar; motile rods, which are Gram-negative, oxidase-negative and catalase-negative. The culture was partly identified by phylogenetic analysis of cloned rDNA sequences. The phylogenetic analysis showed that at least two major groups of bacteria are present. One group of bacteria shows 70–80% similarity (based on 16S rRNA gene sequence data) with the Bacteroides-Cytophaga group, and one group consists of members of the β-subclass of the Proteobacteria.

Phenol alkylation with methanol: effect of sodium content and ammonia selective poisoning of an HY zeolite

Sodium exchange and ammonia selective poisoning of the acid sites of an HY zeolite (Si/Al=20) were carried out and their effects on the catalytic properties for the alkylation of phenol with methanol (200‡C, 1 atm and N2/reactants molar ratio of 4) were evaluated. Results show that the reaction is highly sensitive to the number and strength of the acid sites of the catalyst. A decrease in the number of acid sites by sodium exchange of the protons or by ammonia selective poisoning produces important changes in the selectivity of the reaction. In fact, a high increase in the anisole/cresol ratio is observed as the percentage of exchanged sodium in the zeolite increases, while the ammonia selective poisoning shows that at low desorption temperatures (⩽250‡C) only anisole is formed while at higher desorption temperatures both anisole and cresols were observed. These results show that anisole formation requires sites with lower acid strength compared to those necessary for cresol formation.

Synthesis of cresols by applying H 2O 2 fuel cell reaction

A H 2O 2 fuel cell system was applied for the synthesis of cresols from toluene. Partial oxidation of toluene was initiated by an active oxygen generated on the cathode during H 2O 2 fuel cell reaction. The selective oxidation of toluene to cresols has been effected by using the cathode of carbon black and diluted electrolyte (<0.5 M, H 3PO 4). The cathode of active carbon added with FeCl 3 was also favorable for the synthesis of cresols. The mixture of carbon whisker and FeCl 3-added active carbon enhanced the rate of cresol formation.