Study Of Catalyst Deactivation Research Articles

Nanocrystallite Zeolite BEA for Regioselective and Continuous Acetyl Functionalization of Anisole Using Acetic Anhydride: Catalyst Deactivation Studies.

Ultrasonic pretreatment of gel composition followed by hydrothermal synthesis produces the nanocrystallite zeolite beta (ZB) with crystal sizes of 10.3, 22.6, and 9.1 nm for ZB-1, ZB-2, and ZB-3, respectively. The effect of ultrasonic pretreatment and the (SiO2/Al2O3) ratio of gel composition on physical, textural properties, and also on the catalytic activity of ZB catalysts with increasing time on stream (TOS) was investigated. The specific surface area and mesopore volume for ZB-1, ZB-2, and ZB-3 are 438, 380, and 429 m2/g and 0.17, 0.05, and 0.14 cm3/g, respectively. The activity studies of ZB-1 and ZB-3 catalysts were confirmed that the anisole conversion initially increased with TOS until it attained the maximum value and then started decreasing further with TOS due to the deactivation of the catalyst caused by the strong interaction of the product with the acidic sites in the mesopore region. However, in the case of ZB-2, the anisole conversion (>45%) was sustained for a longer TOS due to its smaller particle size, low mesopore volume, and more acidic sites in the micropore volume that are inclusively made for retardation in the catlytic deactivation rate. The CHNS and TGA analysis of the spent catalysts confirm that ZB-1 and ZB-3 catalysts are susceptible for a significant coke formation attributed due to strong product retention in their large mesopore volume, which lead to the catalytic deactivation.

Catalytic co-conversion of glycerol and oleic acid to bio-aromatics: Catalyst deactivation studies for a technical H-ZSM-5/Al2O3 catalyst

The catalytic co-conversion of glycerol and oleic acid (45/55 wt%) to bio-based aromatics (benzene, toluene, and xylenes, bio-BTX) over a technical H-ZSM-5/Al2O3 catalyst in a fixed-bed reactor was investigated with special attention to catalyst deactivation phenomena. The spent catalysts after a time on stream (TOS) of 12 h were regenerated by an ex-situ oxidative treatment to remove coke and reused for another run. In total, 5 reaction-regeneration cycles were performed. The performance and characteristics of the fresh and regenerated catalysts were determined to identify and quantify the effects of co-feeding on catalyst stability and regenerability. The performance of the catalyst changes upon the number of reaction-regeneration cycles. Despite a negative effect on the peak BTX yield, a remarkable improvement in catalyst stability was found, leading to higher BTX productivity (1260–1505 gBTX gcat-1 for the regenerated catalysts during a TOS of 12 h vs. 834 gBTX gcat-1 for the fresh one during a life-time of 11 h). Detailed catalyst characterization studies show irreversible changes in the catalyst structure after reaction-regeneration cycle(s), such as textural property, crystal structure, framework, and acidity, which impact catalyst performance.

A time- and space-resolved catalyst deactivation study on the conversion of glycerol to aromatics using H-ZSM-5

A time- and space-resolved deactivation study on the conversion of glycerol to aromatics over H-ZSM-5 was performed. For this purpose, glycerol was vaporized/pyrolyzed in a pyrolysis section followed by a catalytic aromatization step. Benchmark performance showed an induction period of ca. 20 min, followed by a rather constant BTX yield of ca. 25.4 ± 2.2C.% for 3–4 h time on stream (TOS). Subsequently, a rapid drop in BTX yield was observed due to catalyst deactivation. Severe coking leads to coverage of catalyst surface area and blockage of micropores, particularly at the entrance of the catalyst bed at short TOS, indicating the presence of an axial coke gradient in the fixed bed reactor. At longer TOS, coke was formed throughout the bed and negligible BTX yield was shown to be associated with the presence of coke at all bed positions. Besides coking, the acidity of the catalyst was also reduced, and dealumination occurred, both with a similar time–space evolution. The results were explained by a conversion-zone migration model, which includes a deactivation zone (with severely coked catalyst), a conversion zone (BTX formation), and an induction zone (a.o. (de-)alkylation reactions), and describes the time- and space-resolved evolution of coking and relevant changes in other catalyst characteristics.

Experimental studies of catalyst deactivation due to carbon and sulphur during CO2 reforming of CH4 over Ni washcoated monolith in the presence of H2S

AbstractThis study presents the CO2 reforming of CH4 over Ni coated monolith catalyst at 800°C and 101.325 kPa. The high CH4 to CO2 ratio employed in this study is similar to the CH4:CO2 ratio of >1 found in biogas. Cordierite monolith samples (0.258 channels per m2) washcoated with alumina are used for the experimental purpose. The study considers the combined deactivation effect due to sulphur poisoning and fouling due to carbon deposition. Four different cases with respect to the introduction and removal of H2S are considered. The rate of deactivation due to simultaneous carbon deposition and sulphur poisoning is much faster than the individual poisoning processes. The catalyst shows almost stable operation for 6 h without the presence of in the feed stream. From the conversion studies, it appears that the pre‐treatment of catalyst samples with H2S leads to negligible sulphur coverage. The sulphur poisoning effect is also found to be reversible.

Continuous aqueous phase reforming of wastewater streams: A catalyst deactivation study

This paper reports on the catalytic performance and deactivation in aqueous phase reforming of wastewater streams for H2 production. Brewery wastewater was chosen as representative of this type of effluent. The effect of catalyst support textural characteristics was evaluated using an activated carbon and different modified supports obtained by infiltration and carbonization of a phenolic resol resin into activated carbon. The effect of active phase was evaluated using Pt and PtRe catalysts with different metal molar ratio. At short time on stream values, Pt catalysts supported on modified activated carbon showed higher H2 production than those supported on unmodified activated carbon, indicating that a lower microporosity facilitates the transport of reactants to catalytic active sites and release of reaction products. Bimetallic PtRe catalysts showed higher activity than Pt, particularly using a metal molar ratio of 1:1, which yielded the highest H2 production (117.2 μmol min−1). Despite the different catalysts tested, early and significant deactivation was observed. The characterization of used catalysts allows postulating the adsorption of organic species and/or coke-like matter deposition on the catalysts surface as main causes of deactivation.

Study of catalyst deactivation during 1,3-butanediol dehydration to produce butadiene

Catalyst deactivation and mechanism of coke formation during the gas phase dehydration of 1,3-butanediol were studied on solid acids of different nature: Al2O3, SiO2/Al2O3, HZSM5 and tungstophosphoric acid (TPA) supported on SiO2. All the catalysts deactivated on stream with a significant coke content ranged between 9% and 14% C. Fresh and spent catalysts as well as carbonaceous deposits were thoroughly characterized using different techniques such as N2 physisorption, FTIR spectroscopy, FTIR of adsorbed pyridine, DSC-TGA, GC-MS and MALDI-TOF MS (matrix-assisted laser desorption/ionization time of flight mass spectrometry). The IR spectra of spent and washed (after direct extraction with CH2Cl2) samples and the superficial soluble coke characterized by MALDI-TOF MS showed the different nature of coke formed in each catalyst with carbonaceous products of higher molecular weights on HZSM5 and TPA/SiO2 than on Al2O3 and SiO2/Al2O3. After catalyst dissolution using hydrofluoric acid and extraction with CH2Cl2 both total soluble and insoluble coke were analyzed. Insoluble coke was only detected on TPA/SiO2 and it was attributed to the strength of its Brønsted acid sites. GC-MS chromatograms of total soluble coke showed the presence of aromatic and polyromantic species, that were very alkylated in the case of HZSM5. Particularly, the well differentiated nature of coke on HZSM5 including alkylnaftalenes and alkylantracenes suggested the coke formation by a shape selectivity mechanism.

Inhibiting the Dealkylation of Basic Arenes during n-Alkane Direct Aromatization Reactions and Understanding the C6 Ring Closure Mechanism

Pt/KL is the widely accepted catalyst for aromatizing n-hexane by 1,6 ring closure but encounters deactivation issues when aromatizing higher carbon-number feeds; undergoing extensive dealkylation to give unwanted CH4 and unselective products, as well as over-aromatization to form coke. Here, we report the use of a non-acidic MFI zeolite support, containing excess K+ beyond ion exchange capacity, well dispersed Pt, and high Pt presence inside the pores, for maximising direct n-alkane aromatization selectivity. TGA, catalyst deactivation studies, and characterizations show that the smaller pore sizes and lack of large cages in the MFI support sterically inhibit coke formation inside the pores (0% compared to 4.9% over Pt/KL for n-octane aromatization), which also reduces dealkylation of ethylbenzene and o-xylene under mild conditions to give a more selective product distribution, 86% selectivity by weight towards C6 ring closure compared to 27% for Pt/KL. Additionally, using NH3-TPD, XPS,CO-DRIFTS, and STEM, we show the contribution of excess K+ as an inhibitor of strong acid sites, an indirect Pt electron promoter through improving metal support interaction, and Pt dispersant. This work highlights the alternative use of well-understood zeolitic supports for the highly selective aromatization of n-heptane and n-octane by 1,6 ring closure, increasing the number of potential streams that can undergo direct aromatization, and providing a suitable alternative to Pt/KL.

Revisiting the mechanism of the Fujiwara–Moritani reaction

A new perspective of the Fujiwara–Moritani reaction is presented, including its kinetic profile and catalyst deactivation studies.

Xylene Isomerization Unit Catalyst Deactivation: Quantitative Case Study of an Industrial Unit

The isomerization of xylenes is a catalytic transformation process of metaxylene and ethylbenzene, which aims to restore the balance between both isomers and convert the ethylbenzene to xylenes. The knowledge of the catalytic deactivation behavior between stages of operation or campaigns (catalyst that has undergone successive regenerations and activations) in xylenes isomerization is very important to determine the useful life of the catalyst and, consequently, to improve the estimation of the economic viability to operate the unit, whether with a new or an old kind of catalyst. This work is a preliminary case study of catalyst deactivation, focused on pre-existing industrial data production of xylenes from a unit found in a famous industry known as Braskem, which is located in Brazil. This article involves monitoring a catalyst load throughout its useful life, which has gone through seven consecutive campaigns. The first stage of the work involved the definition of the variables that most influenced the...

Petroleum like biodiesel production by catalytic decarboxylation of oleic acid over Pd/Ce-ZrO2 under solvent-free condition

The Ce/Zr ratio of Pd/Ce-ZrO2 catalysts was systematically changed in order to investigate the effect of oxygen vacancy concentration on their decarboxylation activityunder solvent-free conditions for potential sustainable petroleum like biodiesel production. Pd/Ce0.5Zr0.5O2 exhibited the highest catalytic activity from all other tested catalysts because it contained the highest oxygen vacancy concentration and Pd dispersion, as shown by the X-ray photoelectron spectroscopy, Raman spectroscopy, and CO-chemisorption data. A catalyst deactivation study also showed that both the Pd dispersion and the oxygen vacancy concentration influences the catalytic activity.The catalyst deactivation was found to occur mainly due to Pd sintering, decreases in the BET surface area and Pd dispersion, and partially due to the loss of oxygen vacancies.

Oxidative Carboxylation of 1-Decene to 1,2-Decylene Carbonate

Cyclic carbonates are valuable chemicals for the chemical industry and thus, their efficient synthesis is essential. Commonly, cyclic carbonates are synthesised in a two-step process involving the epoxidation of an alkene and a subsequent carboxylation to the cyclic carbonate. To couple both steps into a direct oxidative carboxylation reaction would be desired from an economical view point since additional work-up procedures can be avoided. Furthermore, the efficient sequestration of CO2, a major greenhouse gas, would also be highly desirable. In this work, the oxidative carboxylation of 1-decene is investigated using supported gold catalysts for the epoxidation step and tetrabutylammonium bromide in combination with zinc bromide for the cycloaddition of carbon dioxide in the second step. The compatibility of the catalysts for both steps is explored and a detailed study of catalyst deactivation using X-ray photoelectron spectroscopy and scanning electron microscopy is reported. Promising selectivity of the 1,2-decylene carbonate is observed using a one-pot two-step approach.

Pd-Catalyzed Aerobic Oxidation Reactions: Strategies To Increase Catalyst Lifetimes.

The palladium complex [(neocuproine)Pd(μ-OAc)]2[OTf]2 (1, neocuproine = 2,9-dimethyl-1,10-phenanthroline) is an effective catalyst precursor for the selective oxidation of primary and secondary alcohols, vicinal diols, polyols, and carbohydrates. Both air and benzoquinone can be used as terminal oxidants, but aerobic oxidations are accompanied by oxidative degradation of the neocuproine ligand, thus necessitating high Pd loadings. Several strategies to improve aerobic catalyst lifetimes were devised, guided by mechanistic studies of catalyst deactivation. These studies implicate a radical autoxidation mechanism initiated by H atom abstraction from the neocuproine ligand. Ligand modifications designed to retard H atom abstractions as well as the addition of sacrificial H atom donors increase catalyst lifetimes and lead to higher turnover numbers (TON) under aerobic conditions. Additional investigations revealed that the addition of benzylic hydroperoxides or styrene leads to significant increases in TON as well. Mechanistic studies suggest that benzylic hydroperoxides function as H atom donors and that styrene is effective at intercepting Pd hydrides. These strategies enabled the selective aerobic oxidation of polyols on preparative scales using as little as 0.25 mol % of Pd, a major improvement over previous work.

Hydroesterification of bio-oils over HZSM-5, BETA and Y zeolites

The primary aim of this research is to study the influence of various experimental parameters on the reaction in order to establish the optimum conditions for which the highest conversion level of zeolite-catalysed oil hydroesterification (two-step reaction: oil hydrolysis and fatty acid esterification) can be achieved. The experimental results indicate that optimising the reaction temperature and stirring rate (providing adequate mass transfer rate and preventing the diffusion limitations) are the main factors to reach into the optimal catalytic performance. An inadequate concentration of water and alcohol can lead to incomplete conversion of the oil during the hydrolysis and fatty acid esterification steps. Exceeding stoichiometric values during hydrolysis (excess H2O) or esterification (excess CH3OH) does not enhance the conversion level of the oil and can act adversely on the extent of hydroesterification. In excess of 95% of the original zeolite activity was recovered via calcination in air during studies of catalyst deactivation.

Study of the Combined Deactivation Due to Sulfur Poisoning and Carbon Deposition during Biogas Dry Reforming on Supported Ni Catalyst

This paper presents a detailed study of catalyst deactivation as a result of simultaneous sulfur poisoning and coke deposition during biogas dry reforming. Experiments are performed at 700 and 800 °C with 5 and 10 ppm of H2S in model biogas with CH4/CO2 = 1.5 and 2.0. To assess the relative effect of chemisorbed sulfur in deactivating the supported Ni catalyst as compared to that of coke deposition, the experiments are performed with and without H2S in the feed. The catalyst deactivation is found to be faster in the presence of H2S. The deactivation due to sulfur chemisorption is not reversible at 700 °C, while at 800 °C the catalytic activity of Ni starts to recover on removing H2S from the feed stream. The results show that the exit CO mole fraction goes up for the sulfur poisoned catalyst which suggests that the reverse water gas shift and coke gasification reactions are not suppressed to the same degree as the reforming reaction. The fresh and the spent catalysts are characterized using XRD, BET, EDS,...

Study of Catalyst Deactivation in Liquid-Phase Hydrogenation of 3-Nitrostyrene Over Au/Al2O3 Catalyst in Flow Reactor

For the first time, we report the results of the study of dynamics of the Au/Al2O3 catalyst deactivation during the selective liquid-phase 3-nitrostyrene (3-NS) hydrogenation in a fixed bed flow reactor. It is shown that the formation of carbonaceous deposits is the main reason of catalyst deactivation, while the leaching of gold from the Au/Al2O3 catalyst or enlargement of the gold particles has not been detected. The content of the carbon deposits on the spent catalyst at the inlet of the reactor is higher than at the outlet and increases as the initial concentration of 3-NS grows. The character of carbonaceous deposits allocation and analysis of reaction products point out to 3-vinylnitrosobenzene as the main source of the Au/Al2O3 catalyst deactivation coinciding with the speculation arising from the kinetic modeling.

Temperature-programmed propane dehydrogenation over Pt–Sn/Al2O3 catalyst: Application in kinetic and catalyst deactivation studies

The kinetics of propane dehydrogenation and catalyst deactivation over Pt–Sn/Al2O3 catalyst was studied by temperature-programmed reaction. Catalytic runs were performed in a fixed-bed quartz micro-reactor both under constant (620 °C) and rising temperature. The reaction temperature was increased from 600 to 650 °C in such a way that the propane conversion remained the same with time over the deactivating catalyst. A model based on single reversible main reaction and first-order concentration-independent deactivation was used. The model was solved and optimized numerically to obtain the kinetic parameters of the main reaction and catalyst deactivation. Activation energies of 72 and 21 kJ/mol were obtained for the main reaction and catalyst deactivation, respectively. Within 150 h-on-stream, both temperature histories showed the same propylene yield, however the constant temperature operation gave this yield at lower propane consumption. The simulated temperature-time profiles for constant propane conversion showed an upward curvature (that is, accelerating type).

The Challenge of Palladium-Catalyzed Aromatic Azidocarbonylation: From Mechanistic and Catalyst Deactivation Studies to a Highly Efficient Process

Azidocarbonylation of iodoarenes with CO and NaN3, a novel Heck-type carbonylation reaction, readily occurs in an organic solvent–H2O biphasic system to furnish aroyl azides at room temperature and 1 atm. The reaction is catalyzed by Xantphos-Pd and exhibits high functional group tolerance. The catalyst deactivation product, [(Xantphos)PdI2], can be reduced in situ with PMHS to Pd(0) to regain catalytic activity. In this way, the catalyst loading has been lowered to 0.2% without any losses in selectivity at nearly 100% conversion to synthesize a series of aroyl azides in 80–90% isolated yield on a gram scale. Alternatively, the ArCON3 product can be used without isolation for further transformations in situ, e.g., to isocyanates, ureas, benzamides, and iminophosphoranes. A detailed experimental and computational study has identified two main reaction pathways for the reaction. For both routes, Ar–I oxidative addition to Pd(0) is the rate-determining step. In the presence of CO in excess, the Ar–I bond is ...

Selective Dehydration of Glycerol to Acrolein: Development of Efficient and Robust Solid Acid Catalyst MUICaT-5

Valorization of bioglycerol to industrially relevant products has been targeted worldwide to make biodiesel production cost competitive. Among several bulk chemicals derived from glycerol, synthesis of acrolein/acrylic acid is one route which is favored for which several catalysts and processes have been proposed in the literature. The present work reports on gas phase dehydration of glycerol to acrolein by using several catalysts and supports. Dodecatungstophosphoric acid supported (DTP) on hexagonal mesoporous silica (HMS) showed promise. It was observed that HMS acted as a better support for acrolein selectivity as compared to K-10 clay and octahedral molecular sieves (OMS). 20% w/w DTP/HMS catalyst resulted in 94% of glycerol conversion and 80% of acrolein selectivity at 225 °C. However, it suffered with severe deactivation due to coke deposition. Various techniques such as NH3-TPD, BET-surface area, SEM image and EDX analysis were used for catalyst deactivation study. Then a new robust catalyst, MUIC...

Hydrogenation of maleic anhydride to succinic anhydride over nickel/clay catalysts

Hydrogenation of maleic anhydride (MA) to succinic anhydride (SA) over Ni/clay catalysts prepared by an impregnation method has been studied at different temperatures, Ni contents, pressures and weighted hourly space velocity (WHSV). The catalytic activity was greatly influenced by the temperature, Ni content, WHSV and pressure. A 97.1 % MA conversion with 99.6 % selectivity to SA was obtained over 5 %wt catalyst at 180 °C and at a pressure of 1 MPa H2. The catalysts were characterized by an array of techniques, including X-ray diffraction (XRD), H2 temperature-programmed reduction (TPR) and thermogravimetric analysis (TGA). XRD and TPR studies showed that nickel was present as Ni2+ species on the support. Increasing the calcination temperature up to 650 °C led to the destruction of the support structure, as observed by TGA, while a calcination temperature of 550 °C gave the best results. Catalyst deactivation studies showed that the catalyst has a long lifetime, the yield of SA remaining better than 90 % even after a reaction time of 60 h. Studies on the catalyst induction showed that the presence or absence of an induction period was determined by the type of hydrogenation catalyst.

A Highly Efficient and Selective Nickel/Clay Catalyst for Liquid Phase Hydrogenation of Maleic Anhydride to Succinic Anhydride

Three Ni-based catalysts with different clay as support were prepared and tested in the hydrogenation of maleic anhydride, among which Ni/clay1 showed best activity and selectivity. Over Ni/clay1 catalyst prepared by impregnation method, 97.14% conversion of maleic anhydride and 99.55% selectivity to succinic anhydride were obtained at 180 .deg. C under a pressure of 1 MPa. Catalytic activity was greatly influenced by the temperature and weighted hourly space velocity. Catalyst deactivation studies showed that this catalyst have a long life time, the yield of MA still higher than 90% even after a reaction time of 60 h. X-ray diffraction (XRD) and H{sub 2} temperature programmed reduction (TPR) were use to investigate the properties of the catalyst. XRD and TPR studies showed that Ni was present as Ni{sup 2+} on the support, which indicated that there was no elemental nickel (Ni{sup 0}) and Ni{sub 2}O{sub 3} in the unreduced samples. The formation of Ni was strong impact on catalytic activity.