Co–ZSM-5 catalysts in the decomposition of N2O and the SCR of NO with CH4: Influence of preparation method and cobalt loading

Co–ZSM-5 prepared via different methods with Co/Al ratios ranging from 0.03 to 0.83 are investigated in both the direct N₂O decomposition and the selective catalytic reduction (SCR) of NO with CH₄. UV–vis and H₂-TPR are used to get an insight in the active species in these reactions. It is observed that in catalysts with low Co loadings (Co/Al < 0.3) Co is predominantly present as mono-atomic Co species, located at ion exchange positions in ZSM-5. Higher Co loadings result in the formation of different kinds of Co-oxides, which constitute the majority of species in the over-exchanged catalysts (Co/Al > 0.5). The mono-atomic species show the highest activity in the direct decomposition of N₂O, whereas the oxidic Co species do not seem to contribute much to the overall decomposition. In the SCR, the Co-oxide species catalyze the combustion of CH₄ whereas the selectivity towards NO reduction is much increased at low Co loadings. Therefore, over-exchange of Co–ZSM-5 does not seem to be favorable for both the direct N₂O decomposition and the SCR of NO with CH₄. Co/Al ratios <0.3 give the best results both in terms of conversion and activity per Co atom in both reactions.     

Methanol interaction with NO2: An attempt to identify intermediate compounds in CH4-SCR of NO with Co/Pd-HFER catalyst

The objective of this work is the study of fundamental common aspects of NO_x catalytic reduction over a Co/Pd-HFER zeolite catalyst, using methanol or methane as reducing agent. Temperature Programmed Surface Reaction (TPSR) studies were performed with reactant mixtures comprising NO₂ and one of the reducing agents.The formation of formaldehyde was detected in both studied reactions (NO₂–CH₄ and NO₂–CH₃OH) in the temperature range between 100 and 220 °C. At higher temperature, when the NO_x reduction process effectively begins, formaldehyde starts to be consumed.Using methanol as reducing agent, nitromethane and nitrosomethane, are detected. At 300 °C these species are consumed and cyanides and iso-cyanides formation occurs. On the contrary, with methane, these last species were not detected; however, there are strong evidences for CH₃NO and CH₃NO₂ formation.Thus, using methanol or methane, similar phenomena were detected. In both cases, common intermediary species seem to play an important role in the NO_x reduction process to N₂.These results suggest that methanol can be considered as a reaction intermediate species in the mechanism of the reduction of NO₂ with methane, over cobalt/palladium-based ferrierite catalysts.     

Catalytic reduction of NH4NO3 by NO: Effects of solid acids and implications for low temperature DeNOx processes

Ammonium nitrate is thermally stable below 250 °C and could potentially deactivate low temperature NO_x reduction catalysts by blocking active sites. It is shown that NO reduces neat NH₄NO₃ above its 170 °C melting point, while acidic solids catalyze this reaction even at temperatures below 100 °C. NO₂, a product of the reduction, can dimerize and then dissociate in molten NH₄NO₃ to NO⁺ + NO₃⁻, and may be stabilized within the melt as either an adduct or as HNO₂ formed from the hydrolysis of NO⁺ or N₂O₄. The other product of reduction, NH₄NO₂, readily decomposes at ≤100 °C to N₂ and H₂O, the desired end products of DeNO_x catalysis. A mechanism for the acid catalyzed reduction of NH₄NO₃ by NO is proposed, with HNO₃ as an intermediate. These findings indicate that the use of acidic catalysts or promoters in DeNO_x systems could help mitigate catalyst deactivation at low operating temperatures (<150 °C).     

Highly active and stable bimetallic Ir/Fe-USY catalysts for direct and NO-assisted N2O decomposition

The current research investigated N₂O decompositions over the catalysts Ir/Fe-USY, Fe-USY and Ir-USY under various conditions, and found that a trace amount of iridium (0.1 wt%) incorporated into Fe-USY significantly enhanced N₂O decomposition activity. The decomposition of N₂O over this catalyst (Ir/Fe-USY-0.1%) was also partly assisted by NO present in the gas mixture, in contrast to the negative effect of NO over noble metal catalysts. Moreover, Ir/Fe-USY-0.1% can decompose more than 90% at 400 °C (i.e. the normal exhaust temperature) under simulated conditions of a typical nitric acid plant, e.g. 5000 ppm N₂O, 5% O₂, 700 ppm NO and 2% H₂O in balance He, and such an activity can be kept for over 110 h under these strict conditions. The excellent properties of bimetallic Ir/Fe-USY-0.1% catalyst are presumably related to the good dispersion of Fe and Ir on the zeolite framework, the formation of framework Al–O–Fe species and the electronic synergy between the Ir and Fe sites. The reaction mechanism for N₂O decomposition has been further discussed on the temperature-programmed desorption profiles of O₂, N₂ and NO₂.     

Steam resistant CoLa-mordenite catalysts for the SCR of NOx with CH4

The stabilization of Co-mordenite catalysts through lanthanum exchange is reported here. The effect of exchange order and calcination conditions upon the reduction of NO_x to N₂ at 500 °C was tracked during 400 h on a stream containing NO_x, CH₄, O₂ and 10% H₂O. Both the fresh and used catalysts were characterized through TPR, Raman spectroscopy, FTIR spectroscopy using CO as probe molecule, and XPS. These techniques revealed that the CoLa-mordenite catalysts which were not affected by the severe hydrothermal treatment showed no sign of Co or La migration out of the exchange positions. Instead, those that rapidly deactivated showed the formation of cobalt oxides and, in some cases, the migration of the cations to other exchange positions. The presence of exchanged lanthanum seems to preserve the integrity of the zeolite structure preventing the migration of cobalt ions with the subsequent formation of cobalt oxides which favors the reaction of methane with O₂, thus decreasing N₂ production.     

Reduction of lean NOx by ethanol over Ag/Al2O3 catalysts in the presence of H2O and SO2

The reduction of lean NOx using ethanol in simulated diesel engine exhaust was carried out over Ag/Al₂O₃ catalysts in the presence of H₂O and SO₂. The Ag/Al₂O₃ catalysts are highly active for the reduction of lean NOx by ethanol but the reaction is accompanied by side reactions to form CH₃CHO, CO along with small amounts of hydrocarbons (C₃H₆, C₂H₄, C₂H₂ and CH₄) and nitrogen compounds such as NH₃ and N₂O. The presence of H₂O enhances the NOx reduction while SO₂ suppresses the reduction. The presence of SO₂ along with H₂O suppresses the formation of acetaldehyde and NH₃. By infrared spectroscopy, it was revealed that the reactivity of NCO species formed in the course of the reaction was greatly enhanced in the presence of H₂O. The NCO species readily reacts with NO in the presence of O₂ and H₂O at room temperature, being converted to N₂ and CO₂ (CO). Addition of SO₂ suppresses the formation of NCO species and lowers the reactivity of the NCO species. However, the reduction of NOx is still kept at high conversion levels in the presence of H₂O and SO₂ over the present catalysts. About 80% of NOx in the simulated diesel engine exhaust was removed at 743 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Integrated coal pyrolysis with CO2 reforming of methane over Ni/MgO catalyst for improving tar yield

A new process to integrate coal pyrolysis with CO₂ reforming of methane over Ni/MgO catalyst was put forward for improving tar yield. And several Chinese coals were used to confirm the validity of the process. The experiments were performed in an atmospheric fixed-bed reactor containing upper catalyst layer and lower coal layer to investigate the effect of pyrolysis temperature, coal properties, Ni loading and reduction temperature of Ni/MgO catalysts on tar, water and char yields and CH₄ conversion at fixed conditions of 400 ml/min CH₄ flow rate, 1:1 CH₄/CO₂ ratio, 30 min holding time. The results indicated that higher tar yield can be obtained in the pyrolysis of all four coals investigated when coal pyrolysis was integrated with CO₂ reforming of methane. For PS coal, the tar, water and char yield is 33.5, 25.8 and 69.5 wt.%, respectively and the CH₄ conversion is 16.8%, at the pyrolysis temperature of 750 °C over 10 wt.% Ni/MgO catalyst reduced at 850 °C. The tar yield is 1.6 and 1.8 times as that in coal pyrolysis under H₂ and N₂, respectively.     

Alumina supported Pt(1%)/Ce0.6Zr0.4O2 monolith: Remarkable stabilization of ceria–zirconia solution towards CeAlO3 formation operated by Pt under redox conditions

A structured Pt(1 wt%)/ceria–zirconia/alumina catalyst and the metal-free ceria–zirconia/alumina were prepared, by dip-coating, over a cordierite monolithic support. XRD analyses and Rietveld refinements of the structural data demonstrate that in the Pt supported catalysts ceria–zirconia is present as a Ce_0.6Zr_0.4O₂ homogeneous solid solution and that the deposition over the cordierite doesn’t produce any structural modification. Moreover no Pt sintering occurs.By comparing the XRD patterns recorded on Pt/ceria–zirconia/alumina and ceria–zirconia/alumina after three redox cycles, it results that Pt, favouring the structural reorganization of the ceria–zirconia into one cubic solid solution, prevents any CeAlO₃ formation. On the contrary, such phase due to the interaction between Ce³⁺ and the alumina present in the washcoat is detected when redox cycles are carried out on the ceria–zirconia metal free.Transmission electron microscopy (TEM) investigations of the redox cycled Pt/ceria–zirconia/alumina catalyst detected ceria–zirconia grains with diameter between 10 and 35 nm along with highly dispersed Pt particles (2–3 nm) strongly interacting with ceria.Scanning electron microscopy (SEM) and EDX analyses, recorded on the redox cycled Pt/ceria–zirconia/alumina washcoated monolith evidence a homogeneous distribution of the active components through the channels even after redox aging.Reduction behaviour and CO oxidation activity are in good agreement with the structural modification of the solid solution induced by the redox cycles and reflect the positive effect of Pt/ceria interaction on the catalytic performances.The effect of redox aging on the NO reduction by C₃H₆, in lean conditions, was investigated over the Pt/ceria–zirconia/alumina monolith. The catalyst shows at low temperature (290 °C) good NO removal activity and appreciable selectivity to N₂.     

N2O decomposition over K-promoted Co-Al catalysts prepared from hydrotalcite-like precursors

N₂O decomposition was investigated over a series of K-promoted Co-Al catalysts. The activity tests showed that doping with K greatly enhanced the catalytic activity of the Co-Al catalyst, and the enhancement was critically dependent on the amount of K and the calcination temperature. When the catalyst had a K/Co atomic ratio of 0.04 and was calcined at 700–800 °C, a full N₂O conversion could be reached at a reaction temperature of 300 °C. Moreover, even under the simultaneous presence of 4% O₂ and 2.6% water vapor, such high-temperature treated K/Co-Al catalyst exhibited high reactivity and stability, with the N₂O conversion remaining at a constant value of 92% over 40 h run at 360 °C. In contrast, non-doped Co-Al catalyst showed a severe activity loss under such reaction conditions. A combination of characterization techniques was employed to reveal the promoting role of K and the effect of calcination temperature. The results suggest that doping with K increases the electron density of Co and weakens the Co–O bond, thus promoting the activation of N₂O on the Co sites and facilitating the desorption of oxygen from the catalyst surface. High-temperature calcinations made the desorption of O₂ proceed more readily.     

Selective Catalytic Reduction of NOx over H-ZSM-5 Under Lean Conditions Using Transient NH3 Supply

The selective catalytic reduction (SCR) of NO _x over zeolite H-ZSM-5 with ammonia was investigated using in situ FTIR spectroscopy and flow reactor measurements. The adsorption of ammonia and the reaction between NO _x , O₂ and either pre-adsorbed ammonia or transiently supplied ammonia were investigated for either NO or equimolar amounts of NO and NO₂. With transient ammonia supply the total NO reduction increased and the selectivity to N₂O formation decreased compared to continuous supply. The FTIR experiments revealed that NO _x reacts with ammonia adsorbed on Brønsted acid sites as NH₄ ⁺ ions. These experiments further indicated that adsorbed -NO₂ ^– is formed during the SCR reaction over H-ZSM-5.     

Effect of ethyleneglycol addition on the properties of P-doped NiMo/Al2O3 HDS catalysts: Part I. Materials preparation and characterization

Phosphorous-doped NiMo/Al₂O₃ hydrodesulfurization (HDS) catalysts (nominal Mo, Ni and P loadings of 12, 3, and 1.6 wt%, respectively) were prepared using ethyleneglycol (EG) as additive. The organic agent was diluted in aqueous impregnating solutions obtained by MoO₃ digestion in presence of H₃PO₄, followed by 2NiCO₃·3Ni(OH)₂·4H₂O addition. EG/Ni molar ratio was varied (1, 2.5 and 7) to determine the influence of this parameter on the surface and structural properties of synthesized materials. As determined by temperature-programmed reduction, ethyleneglycol addition during impregnation resulted in decreased interaction between deposited phases (Mo and Ni) and the alumina carrier. Dispersion and sulfidability (as observed by X-ray photoelectron microscopy) of molybdenum and nickel showed opposite trends when incremental amounts of the organic were added during catalysts preparation. Meanwhile Mo sulfidation was progressively decreased by augmenting EG concentration in the impregnating solution, more dispersed sulfidic nickel was evidenced in materials synthesized at higher EG/Ni ratios. Also, enhanced formation of the so-called “NiMoS phase” was registered by increasing the amount of added ethyleneglycol during simultaneous Ni–Mo–P–EG deposition over the alumina carrier. That fact was reflected in enhanced activity in liquid-phase dibenzothiophene HDS (batch reactor, T = 320 °C, P = 70 kg/cm²) and straight-run gas oil desulfurization (steady-state flow reactor), the latter test carried out at conditions similar to those used in industrial hydrotreaters for the production of ultra-low sulfur diesel (T = 350 °C, P = 70 kg/cm², LHSV = 1.5 h⁻¹ and H₂/oil = 2500 ft³/bbl).     

Cu/Al2O3 catalysts for soot oxidation: Copper loading effect

Cu/Al₂O₃ catalysts with metal loading from 0.64 to 8.8 wt.% have been prepared and characterized by different techniques: N₂ adsorption at −196 °C (BET surface area), ICP (Cu loading), XRD, selective copper surface oxidation with N₂O (Cu dispersion), TPR-H₂ (redox properties), and XPS (copper surface species). The catalytic activity for soot oxidation has been tested both in air and NO_x/O₂. The activity in air depends on the amount of easily-reduced Cu(II) species, which are reduced around 275 °C under TPR-H₂ conditions. The amount of the most active Cu(II) species increases with the copper loading from Cu_1% to Cu_5% and remains almost constant for higher copper loading. In the presence of NO_x, the first step of the mechanism is NO oxidation to NO₂, and the catalytic activity for this reaction depends on the copper loading. For catalysts with copper loading between Cu_1% and Cu_5%, the catalytic activity for soot oxidation in the presence of NO_x depends on NO₂ formation. For catalysts with higher copper loading this trend is not followed because of the low reactivity of model soot at the temperature of maximum NO₂ production. Regardless the copper loading, all the catalysts improve the selectivity towards CO₂ formation as soot oxidation product both under air and NO_x/O₂.     

Preparation and Characterization of Pt/Al-ZSM-5 Catalysts and their Reactivities for the Oxidation of CO with N2O at Low Temperatures

Al-ZSM-5 was prepared by treating H-ZSM-5 with an aqueous solution of Al(NO₃)₃ and used as a support for Pt catalysts. The Pt-loaded Al-ZSM-5 acts as an efficient catalyst for CO oxidation with N₂O at 273 K. TEM investigations revealed that Pt clusters with an average particle size of around 1–1.5 nm were homogeneously dispersed within Al-ZSM-5. Moreover, FT-IR and XPS analyses indicated that the small Al₂O₃ clusters formed within Al-ZSM-5 plays a significant role in the formation of highly dispersed Pt clusters within the pore structure of the ZSM-5 zeolite, leading to the high catalytic activity of Pt/Al-ZSM-5 as compared to Pt/ZSM-5.     

Catalytic activity and long-term stability of palladium oxide catalysts for natural gas combustion: Pd supported on LaMnO3-ZrO2

The catalytic activity and long-term stability of 2% Pd/LaMnO₃-ZrO₂ catalysts for natural gas combustion were deeply investigated. The catalyst, prepared via solution combustion synthesis, was completely characterized (XRD, BET, FESEM/EDS, TPC/TPD/TPR and FT-IR analysis) in the fresh status, and in the aged one, after prolonged treatment under hydro-thermal ageing and S-compounds poisoning (up to 3 weeks of hydro-thermal treatment at 800 °C under a flow of domestic boiler exhaust gases typical composition of 9% CO₂, 18% H₂O, 2% O₂ in N₂, including 200 ppmv of SO₂). An increased catalytic activity towards NG combustion with ageing was detected: the T₅₀, in fact, got lowered from 570 (fresh sample) to 465 °C (after 3 weeks ageing). Highly dispersed Pd centers were predominant on fresh catalyst. Upon ageing, oxygen covered Pd metal particles formed, at the expense of dispersed cationic and zerovalent Pd atoms. The increase in the catalytic activity was associated to the phase modification occurring in the bulk support, where Mn oxides, active towards CH₄ combustion, segregated. Moreover, bands due to sulfate species were detected in aged samples: IR analysis showed that Pd atoms did not interact significantly with these species. The bands of sulfate species decreased in intensity after 3 weeks ageing, likely mostly due to sintering of the catalyst, with the corresponding decrease in the surface area.     

An In Situ ESR Study of Pd/H-ZSM-5 Interaction with Different Adsorbents

In situ ESR at 120–473 K permits to monitor formation of transient paramagnetic ions/complexes (isolated Pd⁺ sites; Pd⁺/H₂O; Pd⁺/C₆H₆) upon interaction of isolated Pd²⁺ cations stabilized by the H-ZSM-5 matrix with different organic compounds and gas mixtures (NO, O₂, H₂O, H₂, propene, benzene). The in situ study provides insight into the elementary steps of redox processes on isolated Pd species in H-ZSM-5 zeolite under realistic conditions. Adsorbed water stabilizes the transient paramagnetic complex and decreases the rate of Pd²⁺ to Pd⁰ reduction by H₂. Strong bonding of NO _x ligands to Pd²⁺ species suppresses the reduction of Pd(II) ions. Sorption of benzene on preoxidized Pd²⁺/HZSM-5 is accompanied by an easy formation of organic cation-radicals and of a Pd⁺/benzene complex, the paramagnetic Pd⁺/benzene structure indicating a surprisingly high resistance to further reduction to Pd⁰. Illumination of the Pd/HZSM-5 by UV-visible light causes no measurable change in the redox properties of the catalyst.     

Study of ruthenium supported on Ta2O5–ZrO2 and Nb2O5–ZrO2 as catalysts for the partial oxidation of methane

Ru-based catalysts supported on Ta₂O₅–ZrO₂ and Nb₂O₅–ZrO₂ are studied in the partial oxidation of methane at 673–873 K. Supports with different Ta₂O₅ or Nb₂O₅ content were prepared by a sol–gel method, and RuCl₃ and RuNO(NO₃)₃ were used as precursors to prepare the catalysts (ca. 2 wt.% Ru). At 673 K high selectivity to CO₂ was found. An increase of temperature up to 773 K produced an increase in the selectivity to syngas (H₂/CO = 2.2–3.1), and this is related with the transformation of RuO₂ to metallic Ru as was determined from XRD and XPS results. At 873 K and with co-fed CO₂ an increase of the catalytic activity and CO selectivity was found. A TOF value of 5.7 s⁻¹ and H₂/CO ratio ca. 1 was achieved over Ru(Cl)/6TaZr. Catalytic results are discussed as a function of the support composition and characteristics of Ru-based phases.     

Nature of Surface Deposits on Sulfated Zirconia Used as Catalyst in the Benzoylation of Anisole

The effects of CO₂, CO and H₂ co-reactants on CH₄ pyrolysis reactions catalyzed by Mo/H-ZSM-5 were investigated as a function of reaction temperatures and co-reactant and CH₄ concentrations. Total CH₄ conversion rates were not affected by CO₂ co-reactants, except at high CO₂ pressures, which led to the oxidation of the active MoC _x species, but CH _x intermediates formed in rate-determining C–H bond activation steps increasingly formed CO instead of hydrocarbons as CO₂ concentrations increased. CO formation rates increased with increasing CO₂ partial pressure; all entering CO₂ molecules reacted with CH₄ within the catalyst bed to form two CO molecules at 950-1033 K. In contrast, hydrocarbon formation rates decreased linearly with increasing CO₂ partial pressure and reached undetectable levels at CO₂/CH₄ ratios above 0.075 at 950 K. CO formation continued for a short period of time at these CO₂/CH₄ molar ratios, but then all catalytic activity ceased, apparently as a result of the conversion of active carbide structures to MoO _x . The removal of CO₂ from the CH₄ stream led to gradual catalyst reactivation via reduction-carburization processes similar to those observed during the initial activation of MoO _x /H-ZSM-5 precursors in CH₄. The CO₂/CH₄ molar ratios required to inhibit hydrocarbon synthesis were independent of CH₄ pressure because of the first-order kinetic dependencies of both CH₄ and CO₂ activation steps. These ratios increased from 0.075 to 0.143 as reaction temperatures increased from 950 to 1033 K. This temperature dependence reflects higher activation energies for reductant (CH₄) than for oxidant (CO₂) activation, leading to catalyst oxidation at higher relative oxidant concentrations as temperature increases. The scavenging of CH _x intermediates by CO₂-derived species leads also to lower chain growth probabilities and to a significant inhibition of catalyst deactivation via oligomerization pathways responsible for the formation of highly unsaturated unreactive deposits. CO co-reactants did not influence the rate or selectivity of CH₄ pyrolysis reactions on Mo/H-ZSM-5; therefore, CO formed during reactions of CO₂/CH₄ mixtures are not responsible for the observed effects of CO₂ on reaction rates and selectivities, or in catalyst deactivation rates during CH₄ reactions. H₂ addition studies showed that H₂ formed during CH₄/CO₂ reactions near the bed inlet led to inhibited catalyst deactivation in downstream catalyst regions, even after CO₂ co-reactants were depleted.     

DRIFTS study of the catalytic N2O reduction by SO2 on FeZSM-5

SO₂ has been recognized as an effective reducing agent for N₂O over iron-containing zeolite catalysts, lowering the operation temperature up to 100 K with respect to the direct N₂O decomposition. This unique behavior contrasts with the common poisoning effect of SO₂ over other active de-N₂O metals (e.g. Co, Cu, Rh, and Ru). The formation of surface sulfates has been generally posed as the main cause for catalyst deactivation by SO₂. Through the use of in situ infrared spectroscopy (DRIFTS), we show that steam-activated FeZSM-5 indeed builds up stable sulfate species during the N₂O + SO₂ reaction. Significant amounts of sulfur were detected in the used catalyst by elemental analysis and X-ray photoelectron spectroscopy. However, the enhanced N₂O conversion is remarkably stable, indicating that the reducing action by SO₂ and the sulfation of the surface are decoupled. The resulting sulfate species are thus spectators in the catalytic process and do not block or alter the structure of the active sites for N₂O reduction and decomposition.     

Improvement of coke resistance of Ni/Al2O3 catalyst in CH4/CO2 reforming by ZrO2 addition

This work investigates the improvement of Ni/Al₂O₃ catalyst stability by ZrO₂ addition for H₂ gas production from CH₄/CO₂ reforming reactions. The initial effect of Ni addition was followed by the effect of increasing operating temperature to 500–700 °C as well as the effect of ZrO₂ loading and the promoted catalyst preparation methods by using a feed gas mixture at a CH₄:CO₂ ratio of 1:1.25. The experimental results showed that a high reaction temperature of 700 °C was favored by an endothermic dry reforming reaction. In this reaction the deactivation of Ni/Al₂O₃ was mainly due to coke deposition. This deactivation was evidently inhibited by ZrO₂, as it enhances dissociation of CO₂ forming oxygen intermediates near the contact between ZrO₂ and nickel where the deposited coke is gasified afterwards. The texture of the catalyst or BET surface area was affected by the catalyst preparation method. The change of the catalyst texture resulted from the formation of ZrO₂–Al₂O₃ composite and the plugging of Al₂O₃ pore by ZrO₂. The 15% Ni/10% ZrO₂/Al₂O₃ co-impregnated catalyst showed a higher BET surface area and catalytic activity than the sequentially impregnated catalyst whereas coke inhibition capability of the promoted catalysts prepared by either method was comparable. Further study on long-term catalyst stability should be made.     

Aromatization of n-hexane over Ga,Mo and Zn modified H-ZSM-5 zeolite catalysts

n-Hexane aromatization was investigated at 500 °C on parent and metal (i.e. Ga, Mo and Zn) modified H-ZSM-5 zeolite catalysts. Conversion reached 88% over H-ZSM-5 and was stable. Addition of metal resulted in lower conversion (< 80%). Formation of aromatic compounds was favored on Ga/H-ZSM-5 (> 35%) and Zn/H-ZSM-5 (> 40%) while H-ZSM-5 and Mo/H-ZSM-5 showed higher cracking activity. Gallium and zinc favored aromatization. At 600 °C a decrease in activity with increasing TOS was observed. A decrease in aromatics selectivity was also observed. The aromatics selectivity with increase in TOS of Ga/H-ZSM-5 (43–27%) and Mo/H-ZSM-5 (35–27%) catalysts was higher than for Zn/H-ZSM-5 (46–7%).