Shape Selective Zeolite Catalyst Research Articles

Directing Highly a-Axis-Oriented ZSM-5 Nanosheets with Pre-estimated Bifunctional Imidazole Cations.

An MFI-topology nanosheet zeolite with a highly a-axis-oriented structure has rarely been reported but with a great potential for industrial applications. Theoretical calculations on the interaction energies between the MFI skeleton and ionic liquid molecules indicated the possibility of preferential crystal growth along a specific direction, according to which highly a-oriented ZSM-5 nanosheets were synthesized from commercially available 1-(2-hydroxyethyl)-3-methylimidazolium and layered silicate sources. The imidazolium molecules directed the structure formation and meanwhile acted as zeolite growth modifiers to restrict the crystal growth perpendicular to the MFI bc plane, which induced unique a-axis-orientated thin sheets with ∼12 nm thickness. The a-oriented ZSM-5 exhibited more competitive propylene selectivity and longer lifetime than bulky crystals in methanol-to-propylene (MTP) reaction. This research would provide a versatile protocol for the rational design and synthesis of shape-selective zeolite catalysts with promising applications.

Selective toluene methylation to p-xylene: current status & future perspective

ABSTRACT Industrially, petroleum naphtha reforming and steam cracking are two major multistep and energy-intensive sources for p-xylene production. Additionally, p-xylene is also produced by selective toluene disproportionation, heavy (C9) aromatics trans-alkylation and isomerization of xylenes. Rapidly changing market dynamics from fuels to petrochemicals coupled with growing petrochemicals demand has led to the further exploration of economical and highly p-xylene selective processes by using surplus low-value aromatics. Methylation of toluene with methanol has been envisaged as one such potential opportunity to produce p-xylene. For the purpose, significant efforts have been made in the past forty years to develop suitable shape selective zeolite catalysts and technologies to make toluene methylation a highly p-xylene selective process. Current paper briefly highlights various advancements in the toluene methylation process development and aims to provide an extensive review of several works put up in the past to design suitable catalysts, catalyst’s limitations and developmental challenges for toluene methylation. Further, this paper provides an useful insight for two competing chemistries of toluene alkylation and side-by-side methanol reactions. Finally, motivated by competitive chemistry of methanol conversion reactions, existing catalytic limitations and novel synthesis opportunities in engineering shape selective zeolite catalysis, a way forward is proposed to arrive at a logical and futuristic catalyst design strategy for p-xylene production via toluene methylation. The proposed strategy is envisaged to offer low-to-moderate catalyst acidity, improved toluene methylation activity, high p-xylene selectivity and improved catalyst life which, otherwise, up till now have been the bottlenecks to develop distinctly economical toluene alkylation to p-xylene process.

Catalyst design strategies towards highly shape-selective HZSM-5 for para-xylene through toluene alkylation

With the shape selective zeolite catalyst, toluene alkylation with methanol to para-xylene (MTPX) technology could produce highly pure para-xylene (PX) in one step. The lower feedstock cost and less energy consumption in products separation make it more competitive compared to the current toluene disproportionation route. Thus, MTPX is regarded as the most reasonable production route for PX production. This article reviews the strategies that applied to the preparation of high-performance catalysts for MTPX, with special focus on the precise control of pore dimension and acid sites distribution in zeolite to achieve the highest selectivity to PX. The outlook of the MTPX catalyst is also proposed to guide the catalyst development in the field.

Deactivation Mechanism and Regeneration Study of Ga–Pt Promoted HZSM-5 Catalyst in Ethane Dehydroaromatization

Direct nonoxidative conversion of ethane to aromatics has become an effective way of upgrading shale gas. Metal-promoted shape selective zeolite catalysts are often used for aromatization. Although the coking issue of the catalysts in ethane aromatization has been reported, the deactivation mechanism and the performance of regenerated Ga–Pt promoted HZSM-5 needs to be further investigated. The objective of this study is to elucidate deactivation mechanism of Ga–Pt promoted HZSM-5 and investigate the feasibility of regenerating deactivated catalysts for commercial viability. When using lower concentration of oxygen (2 vol %) for regeneration, decreased catalyst deactivation rate was observed. The metal particle size, crystalline structures, and acidity are characterized by various analytical instrumentations (TEM, XRD, NH3-TPD). The change of Bronsted acidity was observed on regenerated catalysts. The results showed that metal agglomeration and leaching of Pt from homogeneous Ga–Pt particle were the main causes of deactivation other than coke deposition, indicating that stabilization of bimetallic metal particles on zeolite surface is critical.

Controlling reactive pathways in complex one-pot reactions using a novel shape-selective catalyst with multifunctional active-sites.

A new kind of composite zeolite catalyst containing multi-functional reactive-sites located in different nanopores with individual shape-selectivity was successfully applied to two complex one-pot (including both sequential and parallel) reactions. Every kind of reactant molecule was exactly catalyzed only for its desired reaction, thus the reactive pathways were effectively controlled.

Catalytic Pyrolysis of Torrefied Biomass for Hydrocarbons Production

A simple thermal pretreatment process called torrefaction has shown to be effective in improving the quality of pyrolysis oil in terms of chemical composition. The main objective of this study was to integrate torrefaction with fast pyrolysis process to produce high quality of bio-oil. In this study, the effects of four pyrolysis temperatures (450, 500, 550, and 600 °C) and shape selective zeolite catalyst (H+ZSM-5) on hydrocarbon yield were analyzed. Temperature and catalyst were found to be favorable for aromatic hydrocarbons from pyrolysis of torrefied biomass. The total carbon yield from catalytic pyrolysis of torrefied biomass was 1.45 times the total carbon yield from catalytic pyrolysis of untreated pine. Reaction mechanisms were proposed to understand the production of hydrocarbons from lignin and holocellulose derivatives.

Al-RUB-41: a shape-selective zeolitecatalyst from a layered silicate

A new zeolite catalyst, Al-RUB-41, was synthesized for the first time. It was tested as a catalyst in methanol amination, and showed a shape-selective performance that results in a highly favorable product distribution. The shape-selective nature was also evidenced by using Pt-Al-RUB-41 as a bifunctional catalyst for decane hydroconversion. With its unique pore architecture and remarkable shape-selective character, Al-RUB-41 presents a significant commercial potential in industrial catalysis.

Development of Diethanolamine Selective Production Process Using Shape-Selective Zeolite Catalyst

Ethanolamines are conventionally produced on an industrial scale exclusively by the reaction of ethylene oxide (EO) with an aqueous solution of ammonia. The reaction is a typical consecutive reaction with three steps [NH3 → NH2(CH2OH) → NH(CH2OH)2 → N(CH2OH)3]; therefore, it is difficult to produce diethanolamine with high selectivity. We developed a catalytic process for selective diethanolamine production from EO and anhydrous ammonia using a ZSM-5 zeolite catalyst modified with rare earth elements. This highly active catalyst was able to recognize the difference at molecular level between diethanolamine and triethanolamine. We also succeeded in producing a binderless molded zeolite catalyst having a shape suitable for a fixed-bed reactor. This catalyst does not give problematic impurities due to undesirable reactions over binders. The catalyst deterioration was overcome by developing a regeneration process using high temperature and high-density ammonia gas as a rinse medium.

Elucidation of the catalytic cracking pathway for unsaturated mono-, di-, and triacylglycerides on solid acid catalysts

Heterogeneous catalytic transformation of lipids to transportation fuels offers a unique opportunity to provide sustainable energy while utilizing the current petroleum refining infrastructure. The reaction chemistry for the heterogeneous catalytic cracking of unsaturated acylglycerides was studied. Mono-, di-, and triolein, which are acylglycerides with oleic acid as the fatty acid constituent, were reacted at 400 °C over H +ZSM-5, faujasite, and silica–alumina catalysts. Reactions were carried out using a pulse-type microreactor utilizing online GC analysis. This technique allowed real time evaluation of reaction products using mass spectrometry and quantitation using a thermal conductivity detector. Selected products of these reactions were further reacted in an effort to elucidate the reaction pathway for producing green fuels from unsaturated lipids. The results indicated the removal of the heteroatom from the oxygenated feedstock by formation of CO and CO 2. The shape-selective zeolite catalysts (i.e. H +ZSM-5 and faujasite) promoted the formation of aromatic compounds as tertiary cracking products. Silica–alumina, an amorphous catalyst, promoted the formation of linear dienes. A reaction scheme has been proposed for the deoxygenation of lipid compounds. These results reveal the potential of using lipid feedstocks for transportation fuels.

High Selectivity Production of Propylene from n-Butene: Thermodynamic and Experimental Study Using a Shape Selective Zeolite Catalyst

Propylene production by n-butene catalytic cracking was studied. Thermodynamic analysis and experimental results showed that a shape-selective catalyst, SAPO-34, with a small pore diameter and weak external acidic sites, can increase the propylene yield and selectivity to 48% and 66%, respectively, from the values of 31% and 36% over a ZSM-5 zeolite by inhibiting the formation of isobutene and other hydrocarbons whose dynamic diameters are larger than isobutene. The optimal temperature for the maximum equilibrium yield of propylene decreases from 600 to 550 °C. The effect of temperature, weight hourly space velocity and time-on-stream in the n-butene cracking process were also studied.

Tert-Butylation of toluene with isobutylene over zeolite catalysts: Influence of water

Abstract tert-Butylation of toluene with isobutylene in the liquid phase was studied over large pore zeolite catalysts (H-MOR CBV 21A with Si/Al = 10.5 and H-BEA CP 814E with Si/Al = 12.5) and over cerium modified parent zeolite H-MOR with 2 wt.% of cerium. The influence of catalyst and different amount of added water on tert-butylation of toluene with isobutylene as alkylating agent on catalytic activity and para-selectivity was studied. H-MOR was slightly more active than H-BEA when tert-butylation of toluene with isobutylene in the liquid phase was carried on in the absence of water (45% and 40% conversion of toluene, respectively) at 180 °C after 8 h with para-selectivity for both catalysts near 68%. When different amount of water was added to the reaction mixture (0–200 mmol) the maximum conversion increased significantly in the case of both catalysts H-MOR and H-BEA and it was obtained at 120 mmol of water/40 mmol of toluene. At optimum amount of added water (120 mmol/40 mmol of toluene) the conversion over H-MOR and H-BEA of toluene reached 60% and 66% respectively which is maximum at given reaction conditions. Maximum constant para-selectivity for both catalysts was near 90% (93% for H-MOR and 90% for H-BEA respectively for maximum amount of added water (200 mmol/40 mmol of toluene)). The positive influence of optimal amount of added water on catalytic activity and para-selectivity in tert-butylation of toluene with isobutylene in the liquid phase over H-MOR and H-BEA is shown in this paper. para-Selectivity increased monotonically within studied range of added water. The influence of water on coke deposits on catalysts was demonstrated by TGA analyses which clearly demonstrated that added water has inhibition effect on carbon deposition. tert-Butylation of toluene with isobutylene over shape-selective zeolite catalysts H-MOR and H-BEA can be an ecofriendly process for industrial preparation of 4-tert-butyltoluene which is important intermediate product for fine chemicals.

A priori selection of shape-selective zeolite catalysts for the synthesis of 2,6-dimethylnaphthalene

Modeling tools based on molecular mechanics and molecular dynamics were used for selecting shape-selective zeolite catalysts for the synthesis of 2,6-dimethylnapthalene (2,6-DMN) through the alkylation of naphthalene (NAPH) or via isomerization of other DMN isomers. A number of medium- (MFI and EUO) and large-pore zeolites ( ∗ BEA, MOR, MAZ, FAU, LTL, OFF, and MTW) were considered and for each of them the minimum energy pathways for the diffusion of naphthalene, 1- and 2-methylnapthalene (MNs), and 1,5-, 1,6-, 2,6-, and 2,7-dimethylnapthalene (DMNs) were computed. The results of the simulations indicated that the diffusion of MNs and DMNs isomers in the medium-pore zeolites is impeded by high-energy barriers, leading to the conclusion that this kind of structure can be used neither in the isomerization nor in the alkylation reaction. In contrast, large-pore zeolites are more promising though their behavior strongly depends on the effective size of the pore openings. Among them, MTW was predicted to be the most promising candidate for the selective alkylation of NAPH to 2,6-DMN. In fact, the simulations indicated high-energy diffusion barriers not only for molecules bearing a CH 3 group in the α-position but also for the undesired 2,7-DMN molecule. Catalytic tests, performed in the presence of 1,2,4-trimethylbenzene as a solvent, confirmed the prediction since MTW gave the highest 2,6-DMN yields with a 2,6-/2,7-DMN ratio in the range 2.0–2.6, well above the thermodynamic value of ≈1 obtained with the other zeolites. The good catalytic performances of MTW were explained by the fact that, unique among the large-pore zeolites considered, this zeolite showed a better stabilization of the 1,1-diarylmethane intermediate molecules leading to 2-MN, 2,6-DMN, and 2,7-DMN. Their formation can be considered more probable than for those deriving from the electrophilic attack of the benzyl carbocation in the α-position of the naphthalene ring.

Developing the molecular modelling of diffusion in zeolites as a high throughput catalyst screening technique.

Molecular modelling techniques have been used to screen zeolite catalysts for their suitability for organic synthesis. For example, we have used these techniques to study the alkylation of aromatic molecules which are important in the fine-chemical and drug industries. A survey of all such efforts is reviewed in this article. The application of molecular modelling techniques in a systematic manner is an efficient first step in the design of zeolite catalysts. As a qualitative screening tool, molecular graphics is used to visualize how well the reactant and product molecules fit inside the pores of the zeolites. Using a hybrid of several molecular modelling methods, which combines molecular dynamics (MD) and Monte Carlo methods with energy minimization, it is possible to determine the minimum energy locations of the molecules inside the zeolites cages. The minimum energy configurations determined by this hybrid method are taken as a starting point for diffusion of the molecules through the zeolite channels. When a molecule is allowed to diffuse through zeolite channel, the molecule attains some maxima and minima in its diffusion energy profile. From the differences between a maximum and a minimum energy configuration, the diffusion energy barrier for the molecule can be calculated in the zeolites. By comparing the diffusion energy barriers for various isomers of a molecule in different zeolites, it is possible to find out the most suitable zeolite for achieving the required shape-selectivity. In addition, factors influencing the diffusivity of the molecules and consequently the shape selectivity are derived. The list of factors and their relative importance are analysed to derive valuable guidelines to design shape-selective zeolite catalysts for a given reaction. Thus, the ultimate aim of these studies is to develop a high throughput computational screening process for the selection of shape-selective zeolite catalysts for various reactions. The dynamic behaviour of molecules inside the pores of zeolites can be studied using MD methods. Since MD is computationally time consuming, it is more efficient to screen the possible zeolite catalysts by energy minimization methods and then perform MD in specific zeolites. More accurate values of diffusivity of the molecules can be calculated using MD methods, and these values can be correlated with the shape-selectivity observed experimentally and /or derived from diffusion energy barrier calculations.

Modeling of adsorption and bifunctional conversion of n-alkanes on Pt/H-ZSM-22 zeolite catalyst

The hydroconversion of C6–C9 n-alkanes on Pt/H-ZSM-22 was investigated by measuring and modeling of the adsorption and catalytic properties of this strongly shape-selective zeolite catalyst. Henry adsorption constants and adsorption isotherms of C6–C9 n- and iso-alkanes on H-ZSM-22 were determined with chromatographic techniques and fitted to different models. While n-alkanes have access to the internal pore structure of ZSM-22, only the linear part of the iso-alkanes adsorbs in the pore entrances. Besides pore and pore mouth adsorption, external surface adsorption plays an important role. In the hydroconversion of C6–C9 n-alkanes, nonselective adsorption of n- and iso-alkanes on the external surface of the ZSM-22 crystals determines the concentration of the reacting species and the reaction orders. The skeletal rearrangement reactions occur exclusively in the pore mouths at the external surface of the zeolite crystals. The hydrocracking reactions were modeled with a lumped reaction scheme, accounting for adsorption on the different types of adsorption sites. The best agreement between model and experiments was obtained with an external surface adsorption model.

PERFORMANCE OF ZSM-5 CATALYST IN THE DIMETHYL ETHER TO OLEFINS PROCESS

ABSTRACT The conversion of dimethyl ether (DME) to hydrocarbons is the latter step in the conversion of syngas to hydrocarbons via DME. The shape-selective ZSM-5 zeolite catalyst plays an instrumental part in this reaction in limiting the higher end of the product spectrum. This process, being of an exothermic nature, results in a temperature rise across the catalyst bed causing some hydrocarbons to be deposited on the catalyst as coke. The presence of water as a byproduct in the catalyst environment also enhances the catalyst deactivation. Deactivation of the ZSM-5 catalyst is studied in detail in terms of catalyst performance and life over a period of time. The conversion of DME and the hydrocarbon product distribution are studied as a function of time-on-stream The SiO2/Al2O3molar ratio of the ZSM-5 catalyst is regarded to be important in determining the degree of coke formation as well as the product distribution of the final hydrocarbon product. Catalysts used in aging experiments were studied as to determine the quantity and structure of the deposited coke. Extracted coke from the catalyst was analyzed using gas chromatography/mass spectrometry methods. The coked catalyst was also analyzed using infra-red as welt as x-ray diffraction techniques.

Catalytic conversion of palm oil to fuels and chemicals

AbstractThe conversion of palm oil to hydrocarbons using a shape selective zeolite catalyst is reported in this work. Palm oil was passed over HZSM‐5 catalyst in a fixed bed micro‐reactor and the reactor was operated at atmospheric pressure, a temperature range of 360 to 420°C and weight hourly space velocity (WHSV) of 2 to 4 h−1. The main objective was to study the effect of reaction temperature and oil space velocity on the conversion and selectivity of gasoline range hydrocarbons. The results show that 40 to 70wt% of the palm oil can be converted to aromatics and hydrocarbons in the gasoline, diesel and kerosene range, light gases, coke and water. The maximum gasoline range hydrocarbons yield of 40wt% of total product formed was obtained at 400°C and 2 h−1 space velocity.

Selective catalysts for the production of nitrogen-containing compounds

Herewith are the two processes developed by Nitto, which produce N-containing compounds such as hydrogen cyanide and methylamines. These processes are characterized by unique selective catalysts: an Fe–Sb–O based fluid-bed catalyst for ammoxidation of methanol and a shape-selective zeolite catalyst for ammonolysis of methanol.

Computer-aided search for shape-selective zeolite catalysts for the synthesis of p-isobutylethylbenzene

Molecular modelling studies show that the formation of p-isobutylethylbenzene is possible inside any ‘large pore’ zeolite, while mordenite is the most probable zeolite to achieve maximum selectivity.

ChemInform Abstract: Continuous Catalytic Conversion of Acetylene to Higher Hydrocarbons over a Metal Modified Shape Selective Zeolite Catalyst

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Catalytic conversion of canola oil to fuels and chemical feedstocks Part I. Effect of process conditions on the performance of HZSM‐5 catalyst

AbstractThe conversion of canola oil to hydrocarbons using a shape selective zeolite catalyst is reported in this work. Canola oil was passed over HZSM‐5 catalyst in a fixed bed micro‐reactor and the effects of reaction temperature and oil space velocity on the conversion and selectivity were studied using a statistical experimental design. The results show that 60–95 wt% of the canola oil can be converted to hydrocarbons in the gasoline boiling range, light gases and water. The gasoline fraction contained 60–70 wt% of aromatic hydrocarbons and the gases were mostly C3 and C4 paraffins. Furthermore, the spent catalyst could be regenerated completely at 600°C in 1 h with dry air.