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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Location of MTBE and toluene in the channel system of the zeolite mordenite: Adsorption and host-guest interactions

This paper reports a study of the location of Methyl Tertiary Butyl Ether (MTBE) and toluene molecules adsorbed in the pores of the organophylic zeolite mordenite from an aqueous solution. The presence of these organic molecules in the zeolite channels was revealed by structure refinement performed by the Rietveld method. About 3 molecules of MTBE and 3.6 molecules of toluene per unit cell were incorporated into the cavities of mordenite, representing 75% and 80% of the total absorption capacity of this zeolite. In both cases a water molecule was localized inside the side pocket of mordenite. The saturation capacity determined by the adsorption isotherms, obtained by batch experiments, and the weight loss given by thermogravimetric (TG) analyses were in very good agreement with these values. The interatomic distances obtained after the structural refinements suggest MTBE could be connected to the framework through a water molecule, while toluene could be bonded to framework oxygen atoms. The rapid and high adsorption of these hydrocarbons into the organophylic mordenite zeolite makes this cheap and environmental friendly material a suitable candidate for the removal of these pollutants from water. - graphical abstract: Location of MTBE (a) and toluene (b) in mordenite channels (projection along the [001] direction). Highlights: Black-Right-Pointing-Pointer We investigated the MTBE and toluene adsorption process into an organophilic zeolite mordenite. Black-Right-Pointing-Pointer The presence of MTBE and toluene in mordenite was determined by X-ray diffraction studies. Black-Right-Pointing-Pointer About 3 molecules of MTBE and 3.6 molecules of toluene per unit cell were incorporated into the zeolite cavities. Black-Right-Pointing-Pointer MTBE is connected to the framework through a water molecule. Black-Right-Pointing-Pointer Toluene is directly bonded to framework oxygen atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Toluene Uptake and Outgassing by a 3D-Printed Silicone and the Impact on Mechanical Performance

Silicone elastomers have advantageous physical properties and are widely used in various applications. Additive manufacturing (AM) of silicones provides additional utility by enabling tunable mechanical and functional properties. However, the performance of these elastomers deteriorates over time with exposure to environmental stressors. Organic solvents and volatile organic compounds (VOCs) are stressors that can cause dimensional changes to silicones with exposure and impact the overall function. Yet, the effects of such exposure on mechanical performance, including load response (LR), are not well understood. Here, in this study, we investigated the impact of a nonpolar solvent, toluene, on AM silicone material properties and compressive load. We observed that AM silicones rapidly absorbed toluene and swelled, leading to an increase in relative LR. Toluene concentration and compression did not affect uptake or swelling rates. In contrast, outgassing rates were slower for compressed coupons compared to uncompressed specimens, attributed to geometric constraints and polymer network changes impacting toluene diffusion outward. Compression also pinned the AM silicones at an enlarged state, significantly reducing relative LR after outgassing. Depending on toluene concentrations and compression, AM silicones can remain robust against toluene exposure and recover their initial printing geometry and mechanical performance after toluene outgassing and polymer relaxation.

Materials science↗
DOE OSTI2024

Microwave-Assisted dry reforming of toluene as a model tar compound using low-cost iron catalyst for syngas clean-up

Gasification of waste feedstock such as biomass, waste plastics suffers from high tar yields during hydrogen-rich syngas production. The presence of tars result in lower quality syngas, lower syngas yields, reactor blockage, reactor down time, and costly maintenance. Therefore, removal of tar from syngas during gasification is essential. Catalytic reforming of tars via in-situ syngas cleanup is an effective way of mitigating tars. This work explores the possibility of microwave-assisted catalytic dry reforming of tars for syngas production. Further, due to its chemical complexity, toluene, which is one of the main tar constituents, could be used as a model tar compound. Toluene dry reforming was studied using the Fe/Al 2 O 3 catalyst under CO 2 under the temperature range of 400–700 °C. The toluene reforming reaction was conducted using microwave and conventional thermal reactors. Under microwave irradiation, CO 2 and toluene conversions are boosted to 80% at 500 °C. Hydrogen and carbon monoxide yields were approximately five times and ten times higher in the microwave reactor at 500 °C, respectively, compared to the productions obtained in the conventional fixed-bed reactor at 700 °C. Filamentous carbon was also produced as a valuable side product to improve the economy of this process and such value-added carbon was only observed in the microwave reactor. Three reaction pathways were observed during microwave reaction: the toluene decomposition produces an initial hydrogen and carbon deposit on the catalyst; the formation of methane and benzene suggests toluene hydrodemethylation as a secondary reaction; and toluene hydrogenolysis forms light alkanes such as methane, and through reforming reaction under CO 2 to syngas.

10 SYNTHETIC FUELS↗
NASA NTRS1988

Detailed mechanism of toluene oxidation and comparison with benzene

A detailed mechanism for the oxidation of toluene in both argon and nitrogen dilutents is presented. The mechanism was used to compute experimentally ignition delay times for shock-heated toluene-oxygen-argon mixtures with resonably good success over a wide range of initial temperatures and pressures. Attempts to compute experimentally measured concentration profiles for toluene oxidation in a turbulent reactor were partially successful. An extensive sensitivity analysis was performed to determine the reactions which control the ignition process and the rates of formation and destruction of various species. The most important step was found to be the reaction of toluene with molecular oxygen, followed by the reactions of hydroperoxyl and atomic oxygen with benzyl radicals. These findings contrast with the benzene oxidation, where the benzene-molecular oxygen reaction is quite unimportant and the reaction of phenyl with molecular oxygen dominates. In the toluene mechanism the corresponding reaction of benzyl radicals with oxygen is unimportant. Two reactions which are important in the oxidation of benzene also influence the oxidation of toluene for several conditions. These are the oxidations of phenyl and cyclopentadienyl radicals by molecular oxygen. The mechanism presented successfully computes the decrease of toluene concentration with time in the nitrogen diluted turbulent reactor. This fact, in addition to the good prediction of ignition delay times, shows that this mechanism can be used for modeling the ignition and combustion process in practical, well-mixed combustion systems.

Bittker, David A.↗
DOE OSTI2012

Simulation of toluene decomposition in a pulse-periodic discharge operating in a mixture of molecular nitrogen and oxygen

The kinetic model of toluene decomposition in nonequilibrium low-temperature plasma generated by a pulse-periodic discharge operating in a mixture of nitrogen and oxygen is developed. The results of numerical simulation of plasma-chemical conversion of toluene are presented; the main processes responsible for C{sub 6}H{sub 5}CH{sub 3} decomposition are identified; the contribution of each process to total removal of toluene is determined; and the intermediate and final products of C{sub 6}H{sub 5}CH{sub 3} decomposition are identified. It was shown that toluene in pure nitrogen is mostly decomposed in its reactions with metastable N{sub 2}(A{sub 3}{Sigma}{sub u}{sup +}) and N{sub 2}(a Prime {sup 1}{Sigma}{sub u}{sup -}) molecules. In the presence of oxygen, in the N{sub 2} : O{sub 2} gas mixture, the largest contribution to C{sub 6}H{sub 5}CH{sub 3} removal is made by the hydroxyl radical OH which is generated in this mixture exclusively due to plasma-chemical reactions between toluene and oxygen decomposition products. Numerical simulation showed the existence of an optimum oxygen concentration in the mixture, at which toluene removal is maximum at a fixed energy deposition.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Measurements of Intermediate Species in Fuel-Rich Oxidation of Ethylene, Toluene, and n -Decane

Polycyclic aromatic hydrocarbons (PAHs) are important precursors to the formation of soot and are also pollutant emissions from combustion devices, including internal combustion engines. To understand the formation of PAHs, the low-molecular-weight hydrocarbon chemistry leading to their formation needs to be understood. Toward this goal, fuel-rich oxidation of three different hydrocarbons, i.e., ethylene, toluene, and n-decane, has been investigated in an atmospheric pressure flow reactor at varying temperatures (1000–1350 K), equivalence ratios (φ = 3.0–12.0), and residence times of 0.25–1.5 s. The major C 1 to C 7 intermediates, such as methane, acetylene, ethylene, allene, propyne, propylene, vinylacetylene, 1,3-butadiene, cyclopentadiene, benzene, and toluene, were quantified using a gas chromatograph equipped with a flame ionization detector. The experimental tendency of intermediate species formation, e.g., the dependence of temperature, equivalence ratio, and residence time, was similar in ethylene oxidation and n-decane oxidation. The concentrations of intermediate species up to C 4 were higher in ethylene/n-decane oxidation than toluene oxidation, while a nearly equal or larger amount of C5–C7 species was produced in toluene oxidation. The experimental data were compared with modeling results using a detailed chemical kinetic mechanism. The calculated data using the kinetic model were in agreement with the experimental results. Additionally, a comprehensive kinetic analysis on the reaction pathways of each species was conducted to assess the differences in the oxidation chemistry with the change in the structure of hydrocarbons. In particular, in-depth analysis of benzene formation was performed, elucidating that two benzene formation pathways were important in ethylene and n-decane oxidation: (1) H elimination of the 2,4-cyclohexadienyl radical produced from the isomerization of the 2,4-cyclopentadienylmethyl radical, and (2) dehydrogenation of cyclohexadiene produced from reactions of vinyl radical with 1,3-butadiene. In toluene oxidation, it was found that benzene was primarily produced from toluene through the replacement of the methyl group with hydrogen.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2018

Effect of relative humidity on the composition of secondary organic aerosol from the oxidation of toluene

The effect of relative humidity (RH) on the chemical composition of secondary organic aerosol (SOA) formed from low-NO x toluene oxidation in the absence of seed particles was investigated. SOA samples were prepared in an aerosol smog chamber at < 2 % RH and 75 % RH, collected on Teflon filters, and analyzed with nanospray desorption electrospray ionization high-resolution mass spectrometry (nano-DESI–HRMS). Measurements revealed a significant reduction in the fraction of oligomers present in the SOA generated at 75 % RH compared to SOA generated under dry conditions. In a separate set of experiments, the particle mass concentrations were measured with a scanning mobility particle sizer (SMPS) at RHs ranging from < 2 to 90 %. It was found that the particle mass loading decreased by nearly an order of magnitude when RH increased from < 2 to 75–90 % for low-NO x toluene SOA. The volatility distributions of the SOA compounds, estimated from the distribution of molecular formulas using the “molecular corridor” approach, confirmed that low-NO x toluene SOA became more volatile on average under high-RH conditions. In contrast, the effect of RH on SOA mass loading was found to be much smaller for high-NO x toluene SOA. The observed increase in the oligomer fraction and particle mass loading under dry conditions were attributed to the enhancement of condensation reactions, which produce water and oligomers from smaller compounds in low-NO x toluene SOA. The reduction in the fraction of oligomeric compounds under humid conditions is predicted to partly counteract the previously observed enhancement in the toluene SOA yield driven by the aerosol liquid water chemistry in deliquesced inorganic seed particles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

In vitro Characterization of Phenylacetate Decarboxylase, a Novel Enzyme Catalyzing Toluene Biosynthesis in an Anaerobic Microbial Community

Anaerobic bacterial biosynthesis of toluene from phenylacetate was reported more than two decades ago, but the biochemistry underlying this novel metabolism has never been elucidated. Here we report results of in vitro characterization studies of a novel phenylacetate decarboxylase from an anaerobic, sewage-derived enrichment culture that quantitatively produces toluene from phenylacetate; complementary metagenomic and metaproteomic analyses are also presented. Among the noteworthy findings is that this enzyme is not the well-characterized clostridial p-hydroxyphenylacetate decarboxylase (CsdBC). However, the toluene synthase under study appears to be able to catalyze both phenylacetate and p-hydroxyphenylacetate decarboxylation. Observations suggesting that phenylacetate and p-hydroxyphenylacetate decarboxylation in complex cell-free extracts were catalyzed by the same enzyme include the following: (i) the specific activity for both substrates was comparable in cell-free extracts, (ii) the two activities displayed identical behavior during chromatographic separation of cell-free extract s, (iii) both activities were irreversibly inactivated upon exposure to O 2, and (iv) both activities were similarly inhibited by an amide analog of p-hydroxyphenylacetate. Based upon these and other data, we hypothesize that the toluene synthase reaction involves a glycyl radical decarboxylase. This first-time study of the phenylacetate decarboxylase reaction constitutes an important step in understanding and ultimately harnessing it for making bio-based toluene.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Relative humidity-dependent viscosity of secondary organic material from toluene photo-oxidation and possible implications for organic particulate matter over megacities

To improve predictions of air quality, visibility, and climate change, knowledge of the viscosities and diffusion rates within organic particulate matter consisting of secondary organic material (SOM) is required. Most qualitative and quantitative measurements of viscosity and diffusion rates within organic particulate matter have focused on SOM particles generated from biogenic volatile organic compounds (VOCs) such as α -pinene and isoprene. In this study, we quantify the relative humidity (RH)-dependent viscosities at 295±1K of SOM produced by photo-oxidation of toluene, an anthropogenic VOC. The viscosities of toluene-derived SOM were 2 × 10 ₋1 to ~6 ×10 6 Pa s from 30 to 90%RH, and greater than ~2 × 10 8 Pa s (similar to or greater than the viscosity of tar pitch) for RH ≤ 17%. These viscosities correspond to Stokes–Einstein-equivalent diffusion coefficients for large organic molecules of ~2 ×10 ₋15 cm 2 s ₋1 for 30 % RH, and lower than ~3 × 10 ₋17 cm 2 s ₋1 for RH ≤ 17 %. Based on these estimated diffusion coefficients, the mixing time of large organic molecules within 200 nm toluene-derived SOM particles is 0.1–5 h for 30% RH, and higher than ~100 h for RH ≤ 17%. As a starting point for understanding the mixing times of large organic molecules in organic particulate matter over cities, we applied the mixing times determined for toluene-derived SOM particles to the world's top 15 most populous megacities. If the organic particulate matter in these megacities is similar to the toluene-derived SOM in this study, in Istanbul, Tokyo, Shanghai, and São Paulo, mixing times in organic particulate matter during certain periods of the year may be very short, and the particles may be well-mixed. On the other hand, the mixing times of large organic molecules in organic particulate matter in Beijing, Mexico City, Cairo, and Karachi may be long and the particles may not be well-mixed in the afternoon (15:00–17:00 LT) during certain times of the year.

Song, Mijung↗
NASA NTRS1987

Toluene stability Space Station Rankine power system

A dynamic test loop is designed to evaluate the thermal stability of an organic Rankine cycle working fluid, toluene, for potential application to the Space Station power conversion unit. Samples of the noncondensible gases and the liquid toluene were taken periodically during the 3410 hour test at 750 F peak temperature. The results obtained from the toluene stability loop verify that toluene degradation will not lead to a loss of performance over the 30-year Space Station mission life requirement. The identity of the degradation products and the low rates of formation were as expected from toluene capsule test data.

Havens, V. N.↗
DOE OSTI2018

H-Abstraction reactions by OH, HO 2 , O, O 2 and benzyl radical addition to O 2 and their implications for kinetic modelling of toluene oxidation

Here, alkylated aromatics constitute a significant fraction of the components commonly found in commercial fuels. Toluene is typically considered as a reference fuel. Together with n-heptane and iso-octane, it allows for realistic emulations of the behavior of real fuels by the means of surrogate mixture formulations. Moreover, it is a key precursor for the formation of poly-aromatic hydrocarbons, which are of relevance to understanding soot growth and oxidation mechanisms. In this study the POLIMI kinetic model is first updated based on the literature and on recent kinetic modelling studies of toluene pyrolysis and oxidation. Then, important reaction pathways are investigated by means of high-level theoretical methods, thereby advancing the present knowledge on toluene oxidation. H-Abstraction reactions by OH, HO 2 , O and O 2 , and the reactivity on the multi well benzyl-oxygen (C 6 H 5 CH 2 + O 2 ) potential energy surface (PES) were investigated using electronic structure calculations, transition state theory in its conventional, variational, and variable reaction coordinate forms (VRC-TST), and master equation calculations. Exploration of the effect on POLIMI model performance of literature rate constants and of the present calculations provides valuable guidelines for implementation of the new rate parameters in existing toluene kinetic models.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

The intensity of forbidden torsional transitions in electronic spectra of molecules with a 6-fold barrier: Application to toluenes

Franck-Condon forbidden transitions involving methyl rotor modes are seen in the S{sub 1} ← S{sub 0} spectrum of toluene and toluene-like molecules. The strongest of these rotor transitions (m{sup ″} = 1 → m{sup ′} = 2, m{sup ″} = 0 → m{sup ′} = 3a{sub 1}{sup ″}, and m{sup ″} = 1 → m{sup ′} = 4) have been shown by Walker et al. [J. Chem. Phys. 102, 8718 (1995)] to gain intensity through the rotor equivalent of the Herzberg-Teller mechanism. Despite the m{sup ″} = 0 → m{sup ′} = 3a{sub 2}{sup ″} transition being forbidden in this formalism, it is sporadically observed. We show that this transition derives oscillator strength from incomplete mixing of the −3 and +3 free rotor basis states due to torsion-rotation coupling. Calculations demonstrate that this mechanism quantitatively explains the intensities observed for toluene, including their temperature dependence. Because the −3/+3 mixing is weakest when the torsional barrier height, V{sub 6}, is small, the m{sup ″} = 0 → m{sup ′} = 3a{sub 2}{sup ″} transition increases in intensity as |V{sub 6}| decreases. The temperature and |V{sub 6}| dependencies explain why reports of the 0 → 3a{sub 2}{sup ″} transition have been intermittent. The torsion-rotation coupling mechanism is predicted to also give significant intensity to m = 0 → m = 6a{sub 2}{sup ′} transitions relative to m = 0 → m = 6a{sub 1}{sup ′} transitions and to provide intensity to 0 → 3a{sub 2} transitions in molecules with a 3-fold (V{sub 3}) barrier. Comparison between the observed and calculated rotor band contours shows, unexpectedly, that the 3a{sub 1}{sup ″} constants fail to predict the 3a{sub 2}{sup ″} contour despite these two states being derived from the same free rotor basis states. Comparison with the observed spectrum also reveals differences in the separation of the S{sub 1} 3a{sub 2}{sup ″} and 3a{sub 1}{sup ″} levels. The V{sub 6} value determined from analysis of the high resolution, rotationally resolved m{sup ″} = 0 → m{sup ′} = 3a{sub 1}{sup ″} spectrum overestimates the 3a{sub 2}{sup ″}–3a{sub 1}{sup ″} separation by 0.6 cm{sup −1}. We postulate that this may be due to torsion-vibration coupling. The observed toluene torsion-rotation contours have been modeled to provide estimates of the rotational constants for several of the torsional states.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Decomposition of toluene in a steady-state atmospheric-pressure glow discharge

Results are presented from experimental studies of decomposition of toluene (C{sub 6}H{sub 5}CH{sub 3}) in a polluted air flow by means of a steady-state atmospheric pressure glow discharge at different water vapor contents in the working gas. The experimental results on the degree of C{sub 6}H{sub 5}CH{sub 3} removal are compared with the results of computer simulations conducted in the framework of the developed kinetic model of plasma chemical decomposition of toluene in the N{sub 2}: O{sub 2}: H{sub 2}O gas mixture. A substantial influence of the gas flow humidity on toluene decomposition in the atmospheric pressure glow discharge is demonstrated. The main mechanisms of the influence of humidity on C{sub 6}H{sub 5}CH{sub 3} decomposition are determined. The existence of two stages in the process of toluene removal, which differ in their duration and the intensity of plasma chemical decomposition of C{sub 6}H{sub 5}CH{sub 3} is established. Based on the results of computer simulations, the composition of the products of plasma chemical reactions at the output of the reactor is analyzed as a function of the specific energy deposition and gas flow humidity. The existence of a catalytic cycle in which hydroxyl radical OH acts a catalyst and which substantially accelerates the recombination of oxygen atoms and suppression of ozone generation when the plasma-forming gas contains water vapor is established.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Theoretical Study of the Mechanism Behind the para-Selective Nitration of Toluene in Zeolite H-Beta

Periodic density functional theory calculations were performed to investigate the origin of the favorable para-selective nitration of toluene exhibited by zeolite H-beta with acetyl nitrate nitration agent. Energy calculations were performed for each of the 32 crystallographically unique Bronsted acid sites of a beta polymorph B zeolite unit cell with multiple Bronsted acid sites of comparable stability. However, one particular aluminum T-site with three favorable Bronsted site oxygens embedded in a straight 12-T channel wall provides multiple favorable proton transfer sites. Transition state searches around this aluminum site were performed to determine the barrier to reaction for both para and ortho nitration of toluene. A three-step process was assumed for the nitration of toluene with two organic intermediates: the pi- and sigma-complexes. The rate limiting step is the proton transfer from the sigma-complex to a zeolite Bronsted site. The barrier for this step in ortho nitration is shown to be nearly 2.5 times that in para nitration. This discrepancy appears to be due to steric constraints imposed by the curvature of the large 12-T pore channels of beta and the toluene methyl group in the ortho approach that are not present in the para approach.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Toluene-induced phase transitions in blue phase liquid crystals

Here, we report phase transitions in blue phase-forming liquid crystals (LCs) that are triggered by exposure to toluene vapours. Specifically, we reveal that room-temperature cholesteric phase mixtures of MLC-2142 and S-811 form blue phases (BP I, II and III) with increasing vapour pressure of toluene. To probe the mechanism underlying this observation, we investigated the phase behaviour of mixtures of BP-forming LCs containing a range of non-volatile aromatic compounds (e.g. pyrene). We interpret our observations to indicate that the principal effect of small aromatic compounds is to decrease the energy penalty associated with the formation of disclination lines in BPs. We also conclude that the absorption of toluene into the BP-forming LCs lowers the energy required for the formation of disclination cores in the BP phase, thus allowing the elastically favoured double-twist cylinders to form at lower temperatures. We further show that BP-forming LCs containing pyrene can be used to detect toluene at concentrations below 200 ppm at room temperature. Overall, these results guide the design of LC-based materials that respond to VOCs at concentrations relevant to occupational settings.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1977

Atmospheric analyzer, carbon monoxide monitor and toluene diisocyanate monitor

The purpose of the atmospheric analyzer and the carbon monoxide and toluene diisocyanate monitors is to analyze the atmospheric volatiles and to monitor carbon monoxide and toluene diisocyanate levels in the cabin atmosphere of Skylab. The carbon monoxide monitor was used on Skylab 2, 3, and 4 to detect any carbon monoxide levels above 25 ppm. Air samples were taken once each week. The toluene diisocyanate monitor was used only on Skylab 2. The loss of a micrometeoroid shield following the launch of Skylab 1 resulted in overheating of the interior walls of the Orbital Workshop. A potential hazard existed from outgassing of an isocyanate derivative resulting from heat-decomposition of the rigid polyurethane wall insulation. The toluene diisocyanate monitor was used to detect any polymer decomposition. The atmospheric analyzer was used on Skylab 4 because of a suspected leak in the Skylab cabin. An air sample was taken at the beginning, middle, and the end of the mission.

Shannon, A. V.↗
NASA NTRS1995

Oxidation Mechanisms of Toluene and Benzene

An expanded and improved version of a previously published benzene oxidation mechanism is presented and shown to model published experimental data fairly successfully. This benzene submodel is coupled to a modified version of a toluene oxidation submodel from the recent literature. This complete mechanism is shown to successfully model published experimental toluene oxidation data for a highly mixed flow reactor and for higher temperature ignition delay times in a shock tube. A comprehensive sensitivity analysis showing the most important reactions is presented for both the benzene and toluene reacting systems. The NASA Lewis toluene mechanism's modeling capability is found to be equivalent to that of the previously published mechanism which contains a somewhat different benzene submodel.

Bittker, David A.↗
DOE OSTI2018

High catalytic performance of Fe-Ni/Palygorskite in the steam reforming of toluene for hydrogen production

The inexpensive and abundant material, palygorskite, was used as a promising catalyst support to prepare Fe-Ni/Pal catalysts. Catalytic steam reforming of toluene as a biomass tar model compound over these catalysts was investigated in a fixed-bed reactor under different parameters, including reaction temperatures and S/C molar ratios. The stability and lifetime of Fe 3 Ni 8 /Palygorskite catalyst was evaluated under optimal conditions and its kinetic parameters were determined as well. The fresh and used catalysts were characterized using X-ray diffraction (XRD), H 2 temperature-programmed reduction (H 2 -TPR), transmission electron microscopy (TEM), and Raman spectra. The results showed that the Fe 3 Ni 8 /Palygorskite catalyst with high dispersion was successfully prepared and exhibited superior catalytic performance compared with those of the monometallic catalysts (Fe 3 /Palygorskite and Ni 8 /Palygorskite) and the bare Palygorskite. Increasing the reaction temperature from 500 °C to 700 °C was beneficial for the toluene conversion and gaseous yields. The catalytic activity of Fe 3 Ni 8 /Palygorskite varied distinctly with the increase of S/C molar ratio and reached maximum at the the S/C molar ratio of 1.0. The apparent activation energy of 41.55 kJ mol -1 and the pre-exponential factor of 1.35 × 10 3 m 3 kg -1 h -1 were obtained for Fe 3 Ni 8 /Palygorskite in kinetic studies under optimal reaction conditions, respectively. Here, the carbon deposition analysis of the used catalysts revealed that the formation of graphitic carbon rather than amorphous carbon was the main reason for the deactivation of Fe 3 Ni 8 /Palygorskite catalysts. When ceased the injection of steam into the reaction system, the graphitic carbon would be accelerating formed on the surface of the Fe 3 Ni 8 /Palygorskite and decreased its catalytic activity for toluene conversion. But owing to the water gas shift reaction, the catalytic activity of Fe 3 Ni 8 /Palygorskite seemed to recover gradually to its optimum.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗