Deactivation Of Zeolite Catalysts Research Articles

Synthesis of hierarchical ZSM-11 and its catalytic performances during methanol to propylene

To solve the easy deactivation of zeolite catalyst in methanol to propylene (MTP) reaction, hierarchical ZSM-11 zeolite composed of loosely aggregating ultra-small nanocrystals (∼10 nm) were prepared using vinyltrimethoxysilane-methyl methacrylate (VTMS-MMA) copolymer latex as a “bond blocker”. The structure and texture properties of the as-synthesized zeolite were systematically characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption desorption, NH3-TPD, and thermogravimetric analysis (TG). The results showed that as compared with the parent ZSM-11-0 without adding the latex, the hierarchically porous ZSM-11-x (1 ≤ x ≤ 3) zeolite synthesized with VTMS-MMA copolymer latex had a higher surface area, mesopore volume, and moderate acidity. Due to the nanocrystallization of the primary grain in the polycrystalline aggregates, the micropores channels in the as-synthesized ZSM-11-x (1 ≤ x ≤ 3) were effectively shortened and abundant intercrystalline mesopores resulted from loosely aggregating of the ultrasmall primary crystals were therefore introduced, which offered the optimized ZSM-11-1 catalysts with a longer catalyst life (46 h) and a higher propylene yield (∼40.5 %) in MTP.

Deactivation of Zeolite Catalysts in the Prins Reaction between Propene and Formaldehyde in the Liquid Phase

The Prins reaction between propene and formaldehyde was studied over H-BEA, H-FAU, H-MFI and H-MOR zeolites at 150 °C in liquid phase. It was found that the H-BEA sample is the most active and selective toward buta-1,3-diene; the H-MFI is a potential catalyst for 3-buten-1-ol synthesis, while H-FAU can be used for 4-methyl-1,3-dioxane production. It had been confirmed that zeolite textural and acidic properties influence catalyst behaviour: the acidic properties influence sample activity, while product distribution is controlled by pore volume and effective pore diameter. The sample’s deactivation process had been studied and the kinetic model of deactivation was proposed. It was shown that the deactivation rate for the H-MFI catalyst is four times greater than for the H-BEA catalyst, probably because its strong/weak acid sites ratio is much more high than for the H-BEA.

Side-chain Alkylation of Toluene with Methanol, Modification and Deactivation of Zeolite Catalysts of the Reaction

The review deals with main aspects of the toluene methylation reaction on basic catalysts. The side reactions of decomposition of methanol to CO and H2 on strong basic sites and ring alkylation of toluene on Lewis acid sites (cations of high polarizing ability) hinder obtaining high yields of the target products – styrene and ethylbenzene. Both types of sites are necessary for the course of the target reaction. So optimizing their strength and quantity is an important prerequisite for the selectivity of the side-chain alkylation catalysts. The advantage of fojasite-based systems for this reaction was confirmed by the works of many researchers. However, the possibilities of use of zeolites of other structural types and representatives of a new generation of molecular sieves are being studied, as well as ways of modifying such materials to increase their catalytic efficiency. The main direction of modification is to regulate the balance of acidity and basicity. Effective charge of framework oxygen atoms, which determines basicity of zeolite framework, increases due to the introduction of guest compounds into the catalyst, and this effect is more significant than influence on basicity of ion exchange for cations of elements of low electronegativity. However, the role of this method of modifying in increasing the selectivity remains crucial due to potentiality to decrease the Lewis acidity of cations. Compounds of other elements and transition metals also are used for modification, as well as promotion with metallic copper and silver. Techniques are applied, but not widely, to deprive the external surface of crystallites of active sites. This method of modification is effective for slowing down their deactivation by coke. Acid sites, in particular BAS, are most often distinguished among the sites responsible for coke formation. The mechanism of coke formation in the absence of such centers is also proposed. On the whole, this issue not fully disclosed and requires a deeper study.

FTIR/PLS and SVM multivariate calibrations to determination of the coke amount into the deactivated catalysts and the product of the methanol to gasoline conversion

The rapid deactivation of zeolite catalysts in the methanol-to-gasoline conversion due to the accumulation of carbonaceous species into the pores is a technological and economic problem that has always been considered. In this work, after zeolites framework modification with various metals, the coke formation into zeolites pores and the bulky by-products (C10, C10+), as a precursor of the coke, were determined using the Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT) in the wavenumber range of 1000–2000 and 1000–4000 cm−1, respectively. The results of this method were modeled using linear PLS and non-linear SVM approaches. The TGA and GC–MS were used as a reference method. Before implementing PLS and SVM regression algorithms, preprocessing methods like the baseline correction and the multiplicative scatter correction (MSC) were performed on the spectroscopic data. RMSEP and R2 for coke amount by PLS and SVM algorithm were (0.33, 0.25), (0.96, 0.98), and for organic fraction (bulky by-products) were (0.38, 0.33), (0.95, 0.98) respectively. Owing to the non-linearity of chemical parameters, the nonlinear SVM regression algorithm presents better results with less error in predicting of the coke and bulky hydrocarbons amounts.

Co-pyrolysis of biomass and plastic waste over zeolite- and sodium-based catalysts for enhanced yields of hydrocarbon products

Ex-situ co-pyrolysis of sugarcane bagasse pith and polyethylene terephthalate (PET) was investigated over zeolite-based catalysts using a tandem micro-reactor at an optimised temperature of 700 °C. A combination of zeolite (HZSM-5) and sodium carbonate/gamma-alumina served as effective catalysts for 18% more oxygen removal than HZSM-5 alone. The combined catalysts led to improved yields of aromatic (8.7%) and olefinic (6.9%) compounds. Carbon yields of 20.3% total aromatics, 18.3% BTXE (benzene, toluene, xylenes and ethylbenzene), 17% olefins, and 7% phenols were achieved under optimal conditions of 700 °C, a pith (biomass) to PET ratio of 4 and an HZSM-5 to sodium carbonate/gamma-alumina ratio of 5. The catalytic presence of sodium prevented coke formation, which has been a major cause of deactivation of zeolite catalysts during co-pyrolysis of biomass and plastics. This finding indicates that the catalyst combination as well as biomass/plastic mixtures used in this work can lead to both high yields of valuable aromatic chemicals and potentially, extended catalyst life time.

A study on the performance of coke resistive cerium modified zeolite Y catalyst for the pyrolysis of scrap tyres in a two-stage fixed bed reactor

Catalytic pyrolysis is a useful technique for the conversion of scrap tyres into liquid fuels. Zeolite catalysts were employed in the pyrolysis of scrap tyres for the production of aromatic rich fuel. Deactivation of zeolite catalysts during pyrolysis reaction was investigated which played an important role in the product quality and composition. Herein, the performance of microporous zeolite catalysts and mesoporous MCM-41 catalyst was evaluated in a two-stage fixed bed reactor for the pyrolysis of scrap tyres. Comparative studies showed the increase in the production of aromatic compounds up to 23.7% over zeolite catalyst as compared to 18.7% over MCM-41 catalyst. However, Zeolite Y catalyst exhibited higher coke formation led to the rapid deactivation. The stability of zeolite catalysts is addressed by the incorporation of Cerium metal within the framework of two zeolite catalysts namely Zeolite Y and ZSM-5 through the ion-exchange technique. Parent and spent catalysts were characterised using synchrotron FT-IR spectroscopy, temperature-programmed desorption of ammonia (NH3-TPD), N2 Physisorption, scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectrometry (ICP-OES), energy-dispersive X-ray spectroscopy (EDX), and hydrogen temperature-programmed reduction (H2-TPD). A higher percentage of aromatics were produced over the large pore Zeolite Y. Cerium ion-exchange decreased the formation of coke from 8.1% to 5.7% over submicron and large pore Zeolite Y catalyst. Moreover, naphthalene production decreased over both Ce-Zeolite Y and Ce-ZSM-5.

Deactivation of Zeolite Catalyst H-ZSM-5 during Conversion of Methanol to Gasoline: Operando Time- and Space-Resolved X-ray Diffraction.

The deactivation of zeolite catalyst H-ZSM-5 by coking during the conversion of methanol to hydrocarbons was monitored by high-energy space- and time-resolved operando X-ray diffraction (XRD) . Space resolution was achieved by continuous scanning along the axial length of a capillary fixed bed reactor with a time resolution of 10 s per scan. Using real structural parameters obtained from XRD, we can track the development of coke at different points in the reactor and link this to a kinetic model to correlate catalyst deactivation with structural changes occurring in the material. The "burning cigar" model of catalyst bed deactivation is directly observed in real time.

Coke formation on the surface of Ni/HZSM-5 and Ni-Cu/HZSM-5 catalysts during bio-oil hydrodeoxygenation

Deactivation of zeolite catalysts due to coke deposition is a pronounced challenge in the hydrodeoxygenation (HDO) of bio-oil. This paper reports on the mechanism of coke formation and catalyst regeneration for two catalysts (Ni/HZSM-5, Ni-Cu/HZSM-5). FT-IR, XPS and Raman spectroscopy characterizations indicate that catalyst deactivation can be divided into three main stages: (1) Lewis acid sites in HZSM-5 support are rapidly covered by oxygenated hydrocarbons. The Brønsted acid sites of HZSM-5 donate protons to oxygenates, leading to the formation of carbocations - precursors of soluble coke on the catalyst surfaces. (2) Soluble coke is then stacked to form disordered filament-like carbon strands that are similar to carbon nanotubes or graphite-like structures. (3) Filament-like carbon evolves into graphite carbon. At the same HDO temperature, more graphite particles are found on the Ni/HZSM-5 catalyst than on the Ni-Cu/HZSM-5 catalyst, indicating higher resistance for the coke formation for Ni-Cu/HZSM-5 catalyst.

A Novel Approach for Prediction of Industrial Catalyst Deactivation Using Soft Sensor Modeling

Soft sensors are used for fault detection and prediction of the process variables in chemical processing units, for which the online measurement is difficult. The present study addresses soft sensor design and identification for deactivation of zeolite catalyst in an industrial-scale fixed bed reactor based on the process data. The two main reactions are disproportionation (DP) and transalkylation (TA), which change toluene and C9 aromatics into xylenes and benzene. Two models are considered based on the mass conservation around the reactor. The model parameters are estimated by data-based modeling (DBM) philosophy and state dependent parameter (SDP) method. In the SDP method, the parameters are assumed to be a function of the system states. The results show that the catalyst activity during the period under study has approximately a monotonic trend. Identification of the system clearly shows that the xylene concentration has a determining role in the conversion of reactions. The activation energies for both DP and TA reactions are found to be 43.8 and 18 kJ/mol, respectively. The model prediction is in good agreement with the observed industrial data.

Mechanochemical approach for selective deactivation of external surface acidity of ZSM-5 zeolite catalyst.

The acid sites associated with the external surface of zeolite particles are responsible for undesirable consecutive reactions, such as isomerization, alkylation, and oligomerization, resulting in a lower selectivity to a target product; therefore, the selective modification (deactivation) of the external surface of zeolite particles has been an important issue in zeolite science. Here, a new method for surface deactivation of zeolite catalyst was tested via a mechanochemical approach using powder composer. Postsynthetic mechanochemical treatment of ZSM-5 zeolite causes a selective deactivation of catalytically active sites existing only on the external surface, as a potentially useful catalyst for highly selective production of p-xylene.

Deactivation of zeolite catalysts for benzene oxidation to phenol

Abstract Coking and deactivating experiments were carried out in a fixed-bed reactor for benzene oxidation to phenol (BTOP). The catalyst used in this study was HZSM-5 (SiO 2 /Al 2 O 3 = 20) treated by high temperature steam at 700 °C. Then the catalysts undergoing different reaction time were analyzed and characterized. The amount of coke was measured by TG. The coke components were detected by infrared. At the same time, the main physics properties of the catalyst with coke deposition were characterized. The pores of the catalyst before and after coking were measured by N 2 adsorption at −196 °C. The amount of hexane and cyclohexane adsorption was measured by weight continuous flow. The acid sites of Bronsted and Lewis were characterized by pyridine adsorption-infrared measurements. Our results show that the deactivation of ZSM-5 in the BTOP reaction system is caused by the coke deposition in the mouth of pores and blocking the pores of the catalyst. It can also be found that the present process agrees with most coking processes over ZSM-5 caused by organic compounds, the Bronsted acid sites are the active sites of the coking.

Deactivation of zeolite catalysts used for NOx removal

The deactivation of Ce-zeolite deNOx catalysts has been studied. Catalysts were aged in exhaust gases of a diesel engine and a natural gas engine. The deactivation in real exhaust gas has been compared to deactivation in simulated exhaust gas. Ammonia and urea were used as reducing agent. Deactivated catalysts were characterized with amongst others XPS, XRF and DRIFT. Zeolite deNOx catalysts show different types of deactivation apart from hydrothermal dealumination. Deactivation may occur at low and at higher temperatures. Several depositions were found on the catalysts: coke, CxHy, S, Zn, P, N and Ca. Coke, CxHy and N containing species can be removed by heating under oxygen rich (deNOx) conditions resulting in (partial) recovery of the catalyst activity. The type of lubricating oil used in the internal combustion engine might be an important factor in the deactivation of the deNOx catalyst.

Deactivation of zeolite catalyst in aniline alkylation

Deactivation of zeolite catalyst in aniline alkylation

A percolation approach for the modeling of deactivation of zeolite catalysts by coke formation: diffusional limitations and finite rate of coke growth

Deactivation of a ZSM-5 catalyst by coke formation is modeled in the presence of diffusional limitations. Coke formation starts with the deposition of a coke precursor, proceeds through growth reactions and stops under the influence of termination reactions. Parallel and consecutive coking mechanisms are considered. The influence of the composition of the reaction mixture is investigated. The concentrations of reactants and reaction products and the coke content are obtained as a function of the position inside the catalyst. The overall rate of the main reaction decreases monotonically with increasing coke content of the catalyst. This is not necessarily so for the coking reaction, when the rate of coke growth is large with respect to the rate of deposition of coke precursor.

Deactivation of zeolite catalysts by coke formation

The deactivation of ZSM-5, −11, and −48 in the cracking of mixtures of hexane with resp. propylene and hexadiene was measured in an electrobalance, operated in a differential mode and connected with an on-line gas chromatograph. In this way the deactivation of both the cracking reaction and the coking reaction could be observed. The effect of coke is more pronounced on its own rate of formation than on the rate of the cracking reaction, except with ZSM-48. Differences between the behavior of the three catalysts can be related to their structural characteristics.

A percolation approach for the modeling of deactivation of zeolite catalysts by coke formation

Percolation theory is applied to the modeling of the deactivation of ZMS-5 by instantaneous coke formation leading to site coverage and pore blockage. In the presence of diffusional limitations coke formation of both the parallel and of the consecutive type is considered. The evolution with time of the profiles of reactants and products concentrations and of the coke content inside the catalyst is predicted.

Deactivation of Zeolite Catalysts

Etude du role de la structure d'une zeolite (dimension et forme), et de la localisation des sites actifs affectant la selectivite pendant la desactivation, les effets de diffusion et leur influence sur la selectivite de la forme et l'utilisation d'une zeolite en tant que catalyseur afin d'examiner le processus chimique de desactivation

Spectroscopic investigations on deactivation of zeolite catalysts during reactions of olefins

Coke formation over acidic zeolite catalysts upon reaction of olefins is investigated using in-situ IR spectroscopy, i.e. an IR cell which simultaneously serves as a fixed-bed flow reactor and is attached to a gas chromatograph. Zeolites HY, dealuminated H-MOR with two different Si/Al ratios and H-ZSM-5 are compared. The effects of the number of active sites and the pore volume of the zeolites on the initial rate of coke formation and the final coke level are studied. The final level of coke deposition reflects to some extent the pore volume of the zeolite catalyst. In all cases a considerable amount of coke formed remained inside the pore structure but another fraction was deposited onto the external surface. Both findings were confirmed by sorption measurements on samples before and after loading with coke. Possible mechanisms of deactivation through coke formation, viz, poisoning, consumption or blockage of sides are briefly considered. In-situ IR spectroscopy revealed that at most a small fraction of the active sites of HY, HMOR or HZSM-5 disappeared during coke deposition suggesting that deactivation is caused by site blocking rather than by poisoning or consumption of the acidic centres. Finally, in-situ IR spectroscopy turned out to be a useful tool for discriminating between low-temperature coke (formed below about 500 K) and high-temperature coke (deposited above 500 K).

Factors in deactivation of zeolite catalyst for benzene alkylation by lower olefins

The authors report on a study of catalyst deactivation (prior to oxidative regeneration) in the alkylation of benzene by propylene, as influenced by the reaction medium, the catalyst activation conditions, and the type of REE in the catalyst. The catalysts were prepared by ion exchange of sodium and calcium forms of Y zeolite (SiO/sub 2//Al/sub 2/O/sub 3/ = 4) with solutions of REE nitrates and ammonia. The catalysts were then dried at 120/sup 0/C. The content of residual sodium in the samples was 0.3-0.35% by weight, residual calcium 1.5-2.5% by weight and REE content 12-13% by weight, all calculated as oxides. The experiments were performed in a pulse microcatalytic unit at 200/sup 0/C.