Mordenite-based Catalysts Research Articles

Ion Impregnation Effect of Fe, Cu, Cr-attributed Mordenite on Stearic Acid Cracking

The improvement in the design of mordenite-based catalysts focuses on the present study to fulfill the massive demand for bio-aviation fuel (BAF) as renewable energy. Modification of the mordenite through ionic impregnation of Fe, Cu, and Cr, has supported the mordenite to perform with better efficiency and activity in catalyzing the cracking process of stearic acid. The adjustment on catalytic activity was carried out by simply reacting the catalyst with stearic acid at 190 °C and investigating cracking products with Gas Chromatography-Mass Spectroscopy. The results of the GC-MS test of the cracking product showed the formation of alkane-alkene and aromatic compounds. BAF was selectively obtained (30.27%) when the reaction was catalyzed by FeCuCr/mordenite catalyst. The BAF derived from FeCuCr/mordenite contained hydrocarbons that include xylene, mesitylene, dodecane, tridecane, tetradecane, and pentadecane. However, reduced selectivity was realized (19.85%) when the reaction was catalyzed by nano FeCuCr/mordenite. Its hydrocarbon constituents include benzene, tetradecane, and pentadecane compounds.

Sustainable Upgrade of Bioderived Glycerol to Solketal through Acetalization over Metal-Free Mordenite Catalysts

In the current work, acetalization of crude glycerol to produce valuable solketal, a renewable fuel additive, is studied over metal-free mordenite-based catalysts. The perfect combination of the appropriate acidity and suitable porosity is required to achieve optimum solketal yield from glycerol. The property–activity correlation was established through various physicochemical characterizations, and reaction parameters were optimized to maximize the solketal yield. The modified mordenite catalyst showed exceptionally high catalytic activity toward the acetalization of crude glycerol and as high as 99% yield of solketal was achieved under mild reaction conditions, i.e., a reaction temperature of 60 °C, a time of 4 h, and atmospheric pressure. The catalyst showed tolerance for water and other impurities present in crude glycerol in addition to excellent recyclability up to three cycles without any regeneration treatment. The economical, easy-to-prepare, recyclable, metal-free, moisture-tolerant nature of the catalyst makes it a promising catalyst candidate to be used at a larger scale. The catalytic process has the potential to utilize crude glycerol obtained from biodiesel plants for the synthesis of biofuel additives solketal. This highlights the industrial and environmental significance of this work.

Ethylation of Ethylbenzene with Ethanol over Mordenite-Based Catalysts: Effects of Acidity, Desilication and Kinetics Analysis

Abstract This communication reports the kinetics analysis of ethylation of ethylbenzene (EB) with ethanol over large pore size mordenite catalysts. In this regard, two different catalyst samples are selected with SiO2/Al2O3 = 180 and 21, respectively. The higher acidic sample (SiO2/Al2O3 = 21) is desilicated to study the effects of desilication on the EB ethylation. The EB ethylation experiments are conducted in a fluidized CREC Riser Simulator using equimolar amount of EB and ethanol as feed. Under the studied reaction conditions, diethylbenzene (DEB) is the main product while a small amount of benzene and lighter gases are also produced. In addition to DEB, the higher acidic mordenite sample also produces benzene via dealkylation of EB. On the other hand, the large pore size mordenite sample gives triethylbenzene (TEB) as a secondary alkylation product. The desilicated sample shows slightly higher DEB selectivity but the EB conversion with this sample is low. Power law–based kinetics evaluation also confirms the above observations by showing low activation energy for DEB formation while high activation energies for benzene and TEB formations.

Conversion of heavy reformate into xylenes over mordenite-based catalysts

The conversion of heavy reformate into high-value xylenes was studied over a series of H-mordenite-based catalysts in a fluidized-bed reactor at 400 °C. The results show that methyl-ethyl-benzenes (MEBs) were more reactive than trimethylbenzenes (TMBs) over all the catalysts studied. Mordenite catalyst with higher acid site concentration (M1) favored dealkylation of MEBs while another mordenite catalyst with lower acid site concentration (M2) favored disproportionation of TMBs. Mixing M2 with ZSM-5 (M2Z1) enhanced MEBs conversion (69.2%) and xylenes yield (22.5 wt.%). The conversion of heavy reformate and toluene mixtures over M2Z1 catalyst increased xylenes yield to a maximum at 25.3 wt.% for a feed containing 70:30 heavy reformate and toluene. The results of converting mixtures of 1,2,4-TMB/toluene and heavy reformate/toluene indicate that catalyst acid site concentration plays a key role in promoting desirable transalkylation reactions needed to enhance xylenes yield. The amount of coke formed increased with the acid site concentration of catalysts and more coke laydown was observed during conversion of heavy reformate than 1,2,4-TMB.

Parametric study of dealkylation–transalkylation reactions over mordenite-based bi-functional catalysts

Transalkylation of heavy reformate (96% A 9 and 4% A 10) without addition of toluene was conducted over four bifunctional mordenite-based catalysts at various process conditions using a flow reactor. The effects of (i) molybdenum content (3 vs. 1 wt.%); mordenite content (80 vs. 67 wt.%); and (iii) metal type (Re vs. Mo) were assessed. The composition of products and their trends was scrutinized to determine the influence of the aforesaid parameters on dealkylation–transalkylation reactions. Higher molybdenum content enhanced the methylethylbenzene (MEB) dealkylation as well as trimethylbenzene (TMB) transalkylation, resulting in increased toluene and xylene formation. Higher mordenite content had little effect on either MEB or TMB conversion. Compared to molybdenum-containing catalysts, rhenium-containing catalyst not only exhibited higher MEB dealkylation and TMB transalkylation, but also resulted in higher hydrogen consumption and methane formation. A reaction scheme for the transalkylation of heavy reformate without the addition of toluene is proposed. Among several reactions that occur during this type of a process, de-ethylation of MEBs is kinetically controlled and probable rate-determining step in the overall reaction scheme. A linear correlation between MEB conversion and xylene yield was observed, which also supports the above rationale.

Benzene alkylation with dodecene-1 over micro-mesoporous molecular sieves

The alkylation of benzene with dodecene-1 has been studied over catalysts with a combined micro-mesoporous structure with different amounts of mesopores obtained by the hydrothermal recrystallization of Beta and mordenite zeolites. The main features of the reaction of benzene alkylation with dodecene-1 over the micro-mesoporous catalysts have been established. The formation of transport pores and an increase in the accessibility of acid sites as a result of recrystallization under mild conditions facilitate an increase in the activity, with a high selectivity for linear phenyldodecanes being retained; a higher degree of recrystallization to MCM-41 leads to a decrease in the conversion and selectivity; the mordenite-based catalysts are more active than zeolite Beta.

How to Improve the Selectivity of Zeolitic Catalysts in C8Aromatic Cut Isomerization

The catalysts used in the isomerization processes of the C8 aromatic cut (xylenes and ethylbenzene) generally contain platinum loaded on a mixed binder/zeolite support. Improving these catalysts consists in increasing the ethylbenzene conversion, which is the most difficult step in this transformation, while minimising the secondary side reactions such as ethylbenzene disproportionation or dealkylation, naphthene ring opening and consecutive cracking of the resulting paraffins. Most of the various adopted approaches concern optimisation of the zeolitic phase. The selectivity gain remains modest on conventional mordenite-based catalysts and it seems more appropriate to explore new zeolitic structures. In this context, interesting results have been obtained on EU-1-based catalysts, which selectivate during the stabilisation period and work then in pore mouth. It has been possible to extend this pore mouth catalysis concept to other one-dimensional zeolitic structures of intermediate pore size, such as ZSM-22 and ferrierite. In addition, the selectivity of EU-1 zeolite can be optimised by varying the acidic sites location through the use of special organic templates. Another approach consisted in considering the entire catalyst (zeolitic and metallic phases, possibly associated with an acidic alumina support such as chlorinated alumina), and in identifying the sites responsible for the paraffin formation. The results demonstrate that paraffin cracking mainly follows a bifunctional mechanism, suggesting that the most promising way to reduce the paraffin yield is to act on the zeolite.

An in situ Fourier transform infrared study on the mechanism of NO reduction by acetylene over mordenite-based catalysts

Selective catalytic reduction of NO with acetylene (C 2H 2-SCR) over mordenite-based catalysts (HMOR, 0.5% Mo/HMOR and NaMOR) was investigated by in situ Fourier transform infrared spectroscopy. A possible mechanism was proposed to explain catalytic performance of the mordenite-based catalysts in the C 2H 2-SCR: Nitrosonium ions (NO +) and bidentate nitrate are reactive nitric species towards acetylene at 250 °C. Isocyanate species thus formed are then hydrolyzed to acid amide species that are crucial intermediate of the C 2H 2-SCR. Bridging nitrate species become reactive towards the reductant when reaction temperature increased to 300 °C. Molybdenum loading on HMOR zeolite considerably increased the population of bridging nitrate species and therefore enhanced the title reaction above 300 °C.

Effect of acid treatments on physico-chemical properties and isomerization activity of mordenite

A series of mordenite-based catalysts of varying acidity and metal concentrations were prepared and the effect of physico-chemical properties of these catalysts on the n-hexane isomerization activity was studied. Acid treatment with nitric acid greatly influenced the nature and amount of aluminum in the zeolite characterized by 29Si and 27Al NMR. The microcalorimerty studies of ammonia adsorption clearly indicated the changes in density and strength of acid sites of mordenite upon acid treatment. At optimum conditions of acid treatment the catalyst exhibited improved properties such as acidity and the catalyst gave enthusiastic results claiming 98% selectivity to isomers in n-hexane hydroisomerization reaction. The catalyst and the reaction parameters for activity of Pt/H-mordenite have been discussed in the present paper.

Hydroisomerization of ethylbenzene over bimetallic bifunctional zeolite catalysts

Zeolite-β and mordenite were impregnated with 0.1 wt.% Pt and varying (0, 0.1, 0.3, 0.5 wt.%) amount of Ni. The line broadening XRD analysis indicates that the increasing Ni addition decreases the crystallinity of zeolites. The TEM analysis indicates that the average metal particle size increases with increasing Ni addition. The states of Ni and Pt were analyzed by ESCA. The acidity measurements by both TPD of ammonia and pyridine adsorbed FT-IR spectroscopy show the occupation of some of the acid sites by the added Ni species. Ni addition up to 0.3 wt.% over 0.1 wt.% Pt/H-β and 0.1 wt.% over 0.1 wt.% Pt/H-MOR enhances the ethylbenzene conversion, isomerization selectivity and sustainability of the catalysts. Further Ni addition above the threshold value leads to a drastic drop in activity and isomerization selectivity. Zeolite-β-based Ni–Pt catalysts always show higher activity and selectivity than mordenite-based catalysts.

SCR of NO by Propene on Monometallic (Co or Ni) and Bimetallic (Co/Ag or Ni/Ag) Mordenite-Based Catalysts

Selective catalytic reduction of NO by propene was investigated on monometallic (Co or Ni) and bimetallic (Co/Ag or Ni/Ag) mordenite-based catalysts in the presence of an oxygen excess. Results showed that the catalytic activity of monometallic catalysts prepared from the zeolite sodium form was higher than that for the catalysts prepared from the sodium form. Opposite performances were found for the bimetallic (Co/Ag or Ni/Ag) catalysts. These results were related to both the location and stability of the metal cations, as well as the acid site density. From “in situ” IR results, a first approach to the possible mechanism has been proposed. Bimetallic samples in the acid form could keep up to 80% of the initial activity in the presence of 10% of water in the feed. SO2 inhibited the SCR activity of the catalysts at low temperature (<400 °C), whereas it showed a promoting effect at temperatures higher than 400 °C.

Hydroisomerization of ethylbenzene over bimetallic bifunctional zeolite catalysts: Maximization of xylene production

Zeolite-β and mordenite were impregnated with 0.1 wt.% Pt and varying (0, 0.1, 0.3, 0.5 wt.%) amount of Ni and reduced at 475 °C. The line broadening in the XRD patterns reveals that the increasing Ni addition decreases the crystallinity of zeolites. The catalysts were also characterized by TEM, ESCA and TPD of ammonia and pyridine. The TEM results show that the average metal particle size increases with increasing Ni addition. ESCA studies clearly points to the maximum percentage of Ni reduction in the Pt loaded zeolite-β and mordenite catalysts. The acidity measurements by both TPD of ammonia and pyridine adsorbed FT-IR spectroscopy show that the number of the acid sites of the catalysts decreases upon the addition of the Ni species. Hydroisomerization of ethylbenzene over the Pt–Ni loaded zeolite and mordenite was carried out in the temperature range 250–400 °C. It has been found that the addition of Ni up to 0.3 wt.% over 0.1 wt.% Pt loaded zeolite-β and 0.1 wt.% over 0.1 wt.% Pt loaded mordenite greatly enhances the ethylbenzene conversion, isomerization selectivity and sustainability of the catalysts. Further addition of Ni above the threshold value leads to a drastic reduction in the activity and isomerization selectivity. Zeolite-β-based Ni–Pt catalysts show higher activity and selectivity than mordenite-based catalysts under the optimized reaction conditions.

Hydroisomerization of n-octane over platinum catalysts with or without binder

The catalytic performance for the hydroisomerization of n-octane (conversion, selectivity and yield) of sets of bifunctional catalysts based on mordenite, beta and ZSM-5 zeolites with or without a binder (bentonite) were compared. As hydrogenating–dehydrogenating function, platinum supported by impregnation (1 wt.%) was used. It was found that the activity decreased in the following order: ZSM-5 > beta > mordenite-based catalysts. A decrease in the activity of agglomerated samples, because of the neutralization of the acid sites by the binder, was expected. The activity decrease was significantly high for ZSM-5 zeolite but the opposite effect was observed for beta zeolite. The presence of aluminium extraframework (EFAL) species in the beta agglomerated sample should be the responsible of this behaviour because of a synergetic effect between these EFAL species and the structural Brönsted acid sites causing an increase of the acid strength. The octane isomers selectivity for the agglomerated mordenite and beta samples was very similar to that in the non-agglomerated ones. ZSM-5 agglomerated sample yielded higher isomer selectivity than the non-agglomerated one. The higher neutralization of the acid sites by the binder was the responsible to that because leads to a higher concentration of carbenium ions, which provide the octane isomers. Also, the binder provided meso and macropores to the zeolite where the metal was likely located avoiding a possible pore partial blockage, with the consequently lower diffusional constraint of the reactants.

Ethylbenzene hydroisomerization over bifunctional zeolite based catalysts: The influence of framework and extraframework composition and zeolite structure

The hydroisomerization of ethylbenzene (EB) has been carried out on a series of bifunctional Pt/Al 2 O 3 -zeolite catalysts, in which both the structure (mordenite, beta, Y, ZSM-5, MCM-22) and the chemical composition (for the mordenite and beta samples) of the zeolitic component were varied. Postsynthesis methods such as ion-exchange, steaming and chemical treatments were used to modify the composition of the samples (framework and extraframework Al content and nature of the compensation cation). Both parameters, zeolite structure and chemical composition, were seen to affect the activity and selectivity of the resultant catalysts. Large pore zeolites, particularly mordenite and beta, presented the highest selectivity to the desired isomerization products, i.e., xylenes. In the case of mordenites the textural properties (mainly the mesoporosity), played a key role in determining the activity and selectivity of the catalysts. Both, zeolite acidity and mesoporosity determined the amount of Bronsted sites accessible to the reactant molecules. It was seen that a reduced amount of accessible Bronsted acid sites in the zeolite favored the isomerization of EB with respect to secondary reactions like cracking of the naphthenes and dealkylation. Selectivities to xylenes above 40% at 60% EB conversion were obtained with most of the mordenite-based catalysts. Also, the calcium-exchanged mordenite samples gave larger xylene yields than the corresponding protonic samples. In the case of the Pt/Al 2 O 3 -beta samples, it was seen that formation of xylenes by isomerization of EB is favored in catalysts presenting a reduced density of Bronsted acid sites and a high mesoporosity. Thus, those catalysts prepared from the beta samples obtained by steaming and steaming+acid treatment of the original acidic zeolite were the most selective to xylenes, giving a selectivity close to 40% at ca 60% EB conversion.

Improving the Stability of H–Mordenite forn-Butane Isomerization

The conversion ofn-butane over mordenite-based catalysts in the presence of hydrogen and water was investigated for reaction temperatures between 523 and 623 K. Special attention was given to the influence of Pt upon catalytic activity, selectivity, and stability. With parent mordenite the catalytic activity forn-butane conversion decreased markedly after a short time on stream. Deactivation can be minimized by hydrogen (in the presence of Pt) and water addition. Both measures are thought to reduce the concentration of intermediate olefins in the zeolite pores. The best results with respect to selective conversion ofn-butane to isobutane were obtained for 0.25 wt% Pt on mordenite in the presence of hydrogen. Higher concentrations of Pt in the catalyst are shown to be detrimental forn-butane isomerization, because of increasing selectivity to hydrogenolysis. A detailed mechanistic scheme forn-butane conversion over Pt-containing mordenites is presented.n-Butane conversion is concluded to occur via a bimolecular mechanism involving a complex network of hydrogen transfer, oligomerization/cracking, isomerization, hydrogenation/dehydrogenation, and hydrogenolysis.