Fast Catalyst Deactivation Research Articles

Potentialities of the Direct Catalytic Processing of Methane into in-Demand Chemicals. Review

Literature data are reviewed in the field of catalytic reaction of the direct transformation of methane into marketable chemicals (H 2 , C 2+ hydrocarbons, methanol, formaldehyde and higher oxygenates). At present the processes based on these reactions are not implemented in industry. Catalytic systems providing achievement of the maximal parameters (in the first, the yields of target products) were identified for each of the reactions, and the proximity to their potential commercialization was determined. The processes of synthesis of C 2+ and alkylaromatic hydrocarbons via oxidative condensation (dimerization) of methane and by the reaction of methane with C 3 –C 6 alkanes, respectively, are considered most promising for the semicommercial production in the nearest future. A considerable progress in the development of new zeolite and aluminosilicate modifications makes it possible to solve the problem of the fast catalyst deactivation during olefin methylation to produce hydrocarbons of the gasoline fraction. Implementation of the process of methane pyrolysis to carbon and H 2 is mainly limited by insufficient demand for the obtained types of carbon materials and by the low strength of the available catalysts for fixed catalyst bed processes. The yields of a number of products (methanol, formaldehyde) are not as high as the ones required for the process commercialization. As to the other products (higher oxygenates), a general possibility of their synthesis is only so far demonstrated.

Steam reforming of plastic pyrolysis model hydrocarbons and catalyst deactivation

Catalytic steam reforming of n-hexane, 1-hexene, tetradecane and toluene over a Ni commercial catalyst has been carried out in a fluidized bed reactor at 700°C. These compounds have been selected as model compounds of the volatiles formed in the pyrolysis of waste plastics in order to study in detail the performance of the catalyst in the pyrolysis-reforming of different plastic wastes. High carbon conversions and hydrogen yields are obtained at zero time on stream, with peak values being 96.5% and 82.8%, respectively, when n-hexane is used as model compound. Similar reactivity has been observed for tetradecane and 1-hexene, whereas lower carbon conversion (82%) and hydrogen yields (65%) are obtained for toluene. Concerning catalyst stability, olefinic compounds (1-hexene) and aromatic compounds (toluene) cause faster catalyst deactivation than paraffinic compounds (tetradecane and n-hexane). These disparities are explained by the different nature of the coke deposited and the different potential of the compounds to block Ni active sites, with olefins and aromatics being encapsulating coke precursors (amorphous and structured, respectively) and paraffins being filamentous and inert coke precursors.

Selective Conversion of Glycerol into Propylene: Single-Step versus Tandem Process

Dehydration and catalytic cracking reactions can be combined to convert glycerol into light olefins using solid acid catalysts. The combination is suitable for a single-step process to convert glycerol into light olefins at high temperatures (26–36% selectivity at 873 K). However, large quantities of carbon oxides are produced (31–39% COx selectivity), and catalyst deactivation also occurs. High light olefin selectivity (62–65%) and a smaller quantity of carbon oxides (11–12% COx selectivity) can be obtained by using a tandem process involving the dehydration of glycerol and subsequent catalytic cracking of the dehydration products (mainly acetol and acrolein). Furthermore, the ratio of propylene to ethylene can be adjusted by changing the dehydration catalysts to favor the production of acetol or acrolein: Acetol forms propylene, and acrolein forms ethylene. To overcome the fast deactivation of acid catalysts in glycerol dehydration, the hydrogenolysis and catalytic cracking reactions can be synchronized...

Stable and efficient aromatic yield from methanol over alkali treated hierarchical Zn-containing HZSM-5 zeolites

Fast deactivation of catalyst is the main problem in methanol-to-aromatics (MTA) process. Herein, Zn-containing HZSM-5 zeolites with hierarchical pores (H-Zn/HZSM-5) were prepared by treating directly synthesized Zn/HZSM-5 with NaOH solution. The changes in crystallinity, acidity and textural properties of Zn/HZSM-5 before and after alkali treatment were characterized by X-ray diffraction, NH3-TPD, 27Al MAS-NMR, N2 physisorption, X-ray fluorescence and TEM techniques. MTA reaction under the operating conditions of T = 400 °C and WHSV = 2.5 h−1 showed that the aromatic yield was improved from 41.4% for HZSM-5 to 55.3%. Furthermore, H-Zn/HZSM-5 exhibited a high initial space time yield of 0.62 g gcat−1 h−1 and a long lifetime up to 120 h. These results could be ascribed to the hierarchical pores and the providential acidity, which enhanced the adsorption and diffusion of intermediates/products during the reaction.

ITQ-39 zeolite, an efficient catalyst for the conversion of low value naphtha fractions into diesel fuel: The role of pore size on molecular diffusion and reactivity

ITQ-39, a multipore zeolite with interconnected 12- and 10-ring channel systems, effectively catalyzes the alkylation of two low value naphtha fractions for the production of diesel range alkylaromatics. A catalytic and molecular dynamics study allows us to conclude that its higher selectivity to the desired diesel fraction and, especially, its longer catalyst life as compared to beta or MCM-22, conventionally used as heterogeneous alkylation catalysts, are due to the combined contribution of its small nano-sized crystallites, moderate Brønsted acidity and unique framework topology.The small diffusion coefficients obtained for alkylaromatics on ITQ-39 as compared to those corresponding to the large pore beta zeolite evidence the significant diffusional problems of most of the reactants and products through the channels of the ITQ-39 structure. Thus, alkylation reactions on this zeolite seem to occur mainly on the most external acid sites (external surface, pore mouths), whereas the zeolite structure contributes positively by preventing undesired reactions to occur, which would result in lower selectivity to the monoalkylated products and in a faster catalyst deactivation.

Highly Efficient Process for the Conversion of Glycerol to Acrylic Acid via Gas Phase Catalytic Oxidation of an Allyl Alcohol Intermediate

The conversion of glycerol, the main byproduct of the biodiesel industry, to acrylic acid is one of the most attractive biomass to biochemical processes. It represents millions of tons of market demand. The previous tandem reaction protocol for the conversion of glycerol to acrylic acid via an acrolein intermediate always suffers from fast catalyst deactivation and thus cannot be commercialized. Herein, a novel two-step protocol for the conversion of glycerol to acrylic acid is presented: glycerol deoxydehydration (DODH) by formic acid to allyl alcohol, followed by oxidation to acrylic acid in the gas phase over Mo–V–W–O catalysts. In the second step, supported and unsupported Mo–V–W–O multiple-metal oxide catalysts were used for the transformation of allyl alcohol to acrylic acid and excellent activity as well as selectivity was achieved. Remarkably, the mesoporous silica-supported Mo–V–W–O catalysts showed superb stability on time stream under the optimal reaction conditions with an overall acrylic acid yield of 80%. This study provides a prominent catalytic process for the large scale production of acrylic acid from biorenewable glycerol.

Catalytic steam reforming of volatiles released via pyrolysis of wood sawdust for hydrogen-rich gas production on Fe–Zn/Al2O3 nanocatalysts

Thermo-chemical processing of biomass is a promising alternative to produce renewable hydrogen as a clean fuel or renewable syngas for a sustainable chemical industry. However, the fast deactivation of catalysts due to coke formation and sintering limits the application of catalytic thermo-chemical processing in the emerging bio-refining industry. In this research, Fe–Zn/Al2O3 nanocatalysts have been prepared for the production of hydrogen through pyrolysis catalytic reforming of wood sawdust. Through characterization, it was found that Fe and Zn were well distributed on the surface with a narrow particle size. During the reactions, the yield of hydrogen increased with the increase of Zn content, as Zn is an efficient metal promoter for enhancing the performance of the Fe active site in the reaction. The 20% Fe/Al2O3 catalyst with Zn/Al ratio of 1:1 showed the best performance in the process in relation to the hydrogen production and resistance to coke formation on the surface of the reacted catalyst. All the catalysts showed ultra-high stability during the process and nearly no sintering were observed on the used catalysts. Therefore, the nanocatalysts prepared in this work from natural-abundant and low-cost metals have promising catalytic properties (high metal dispersion and stability) to produce H2-rich syngas with optimal H2/CO ratio from the thermo-chemical processing of biomass.

Effect of addition of a second metal in Mo/ZSM-5 catalyst for methane aromatization reaction under elevated pressures

Non-oxidative methane dehydro-aromatization (MDA) over transitional metal-doped zeolites (i.e. ZSM-5) has a potential to be an alternative for methane transformation processes to higher hydrocarbons. Despite of systematic studies of the effects of the catalyst composition, preparation procedure, pretreatment, and the reaction conditions systematically followed since the pioneering works of the Chinese group in 1993, the suppression of fast deactivation of catalyst by coke deposition was still not solved successfully.In the present work the long-term MDA experiments at 973K and elevated pressures up to 600kPa were carried out with metal-doped Mo/ZSM-5 catalysts. Several Mo-based catalysts doped with various amount of Co, Mn, and Ce were prepared and tested in the MDA reaction. Experimental results are presented in terms of profiles of methane conversion as well as ethylene, benzene, and toluene concentrations as a function of time on stream, accompanied by the TGA analysis of the coke residue accumulated on the spent catalysts. The amount and nature of coke deposits which were influenced by introduction of different metals were also investigated. The Co content of 0.8wt% in Co-Mo/ZSM-5 catalyst was evaluated as optimal for total benzene production. Prolonged experiments showed the evident positive effect of higher reaction pressure on catalyst stability for all tested catalysts. Moreover, the Co–Mo/ZSM-5 catalyst showed better resistance to the deactivation by coke formation in comparison to Mo/ZSM-5 and M–Mo/ZSM-5 (where M=Mn, Ce) catalysts. In addition, the Ce-modified catalyst showed comparable higher production of toluene at elevated pressures.

Benzene removal over a fixed bed of wood char: The effect of pyrolysis temperature and activation with CO2 on the char reactivity

Benzene removal using spruce wood char as catalyst was investigated. The influence of pyrolysis temperature and activation with CO2 on the char structure and reactivity for benzene adsorption and cracking was analyzed. The structural features of the char were examined by the CO2 adsorption technique and Fourier transform infrared spectroscopy (FTIR). The reactivity for benzene removal was investigated using a fixed bed quartz reactor.Surface analysis showed that the microporous char surface area was influenced by the pyrolysis temperature and was almost doubled by activation with CO2.The benzene adsorption capacity of the char decreased with increasing pyrolysis temperature. Activation with CO2 however, increased the fraction of adsorbed benzene by a factor of two and 10 for char produced at 500 and 800°C, respectively. The total microporous surface above 700 m2/g was found to be a good indicator for the reactive char surface for benzene cracking at high temperatures. At 1050°C the main mode of benzene conversion was homogeneous thermal decomposition.We confirmed that wood char has the potential to serve as an effective catalyst for benzene removal. However, benzene decomposed over the charcoal by carbon deposition which led to a fast deactivation of the wood char catalyst.

Small-Scale Biogas-SOFC Plant: Technical Analysis and Assessment of Different Fuel Reforming Options

This paper investigates simulation results of the thermodynamic performance of a 25 kWel small-scale solid oxide fuel cell model fuelled with biogas. Hereby, biogas is produced from a predefined group of substrates, namely, livestock effluents, energy crops, agricultural waste, and organic waste. For the analysis, average methane (CH4) content is assumed to lie between 50 and 60 mol % as large seasonal and daily variations are observed which are independent of used matter. The main biogas contaminants are sulfur compounds, mostly in the form of H2S. Sulfur leads to fast catalyst deactivation in the reformer and fuel cell, which is why an effective gas-cleaning system is established. For this, ZnO and activated carbon are the most practical gas-cleaning solutions for small-scale plants. The energy model of the solid oxide fuel cell plant is designed and analyzed through detailed energy and mass balance calculations throughout all system components and streams. The above-mentioned model is set up in in such...

Effect and behavior of cerium oxide in Ni/γ-Al2O3 catalysts on autothermal reforming of methane: CeAlO3 formation and its role on activity

Nickel supported γ-alumina (Ni/γ-Al2O3) catalysts are well-known to be highly active on the autothermal reforming of methane, but to be unstable due to coke deposition. Cerium oxide (CeO2) is one of promising promoter to overcome the fast deactivation of nickel-based catalysts by coke formation. Herein, catalytic behavior of CeO2 over Ni/γ-Al2O3 catalysts on the autothermal reforming of methane was investigated. The catalytic activity was maintained for 100 h with H2/CO molar ratio of 1.9. The formation of CeAlO3 is observed at the reduction and reaction conditions. In this work, it was found that the formation of CeAlO3 promoted the catalytic oxidation toward CO2 and prevented the formation of α-Al2O3 and nickel-aluminate, resulting in stable activity for autothermal reforming of methane.

Performances of Pd Nanoparticles on Different Supports in the Direct Synthesis of H2O2 in CO2-Expanded Methanol

Catalysts based on Pd supported on SiO2, SBA-15, γ-Al2O3 and N-CNT were investigated for the direct H2O2 synthesis and decomposition/hydrogenolysis in CO2-expanded methanol in batch and semi-batch reactors working at room temperature and a pressure of 6.5 bar. The order of reactivity for the synthesis of H2O2 per g of Pd or for the rate of H2O2 decomposition, or the selectivity to H2O2 does not correlate with the acidity of the support. A relation was observed with the Pd particle sizes, i.e. smaller particles lead to a higher specific activity, but the sample supported on carbon nanotube shows an order of magnitude higher specific activity per g of Pd, indicating the presence of an additional factor attributed to the interaction with the carbon support which determines an intrinsic higher reactivity. However, this higher reactivity corresponds also to a higher activity in the consecutive conversion of H2O2, probably by hydrogenolysis reaction. A rough relation between activity in H2O2 synthesis and in H2O2 conversion was observed in the samples with the different supports, indicating the similar nature of the active sites responsible for the two reactions. Finally, the analysis of the recyclability of the catalysts and transmission electron microscopy (TEM) characterization data after the catalytic tests indicate that the use of CO2-expanded methanol allows improving the catalytic performances in H2O2 direct synthesis due to the enhanced solubility of H2 and O2, but induces a fast catalyst deactivation due to an enhanced mobility and sintering of the supported Pd particles. The effect is present in all the four type of support used.

Oxidative coupling of methane in a fluidized bed reactor: Influence of feeding policy, hydrodynamics, and reactor geometry

Oxidative coupling of methane (OCM) is suggested to be a promising process for the conversion of the abundant natural gas into useful chemicals. However, this reaction faces many drawbacks such as low yields for higher hydrocarbons, fast catalyst deactivation, and huge heat effects of the reaction. Only a well-designed fluidized bed reactor is able to overcome effectively those disadvantages and to provide a satisfactory continuous operation. However, design approaches for fluidized bed reactors are still based on models developed during 70s and 80s, which cannot take into account various hydrodynamic effects on the reactor performance. Thus, a reactor designer has usually to rely on extensive experiments in order to improve the classical fluidized bed reactor design. In this work, the relevance of hydrodynamics, reactor geometry, and feeding policy on the performance of a fluidized bed reactor for the OCM is shown. For this purpose, several case studies of fluidized bed reactors are simulated in full 3D geometry under the same reaction conditions, but with different reactor geometries and feeding policy. These studies show the significance of hydrodynamic parameters for the reactor performance, and moreover, how fluidized bed reactor performance can be improved by a careful study of coupled momentum-mass transport-reaction phenomena. Furthermore, it can be demonstrated that a suitable distributed feeding policy of oxygen provides an improved yield while a traditional fluidized bed reactor design results in an inferior performance among all investigated cases.

Novel α-pinene-derived mono- and bisphosphinite ligands: Synthesis and application in catalytic hydrogenation

Novel mono- and bisphosphinite (−)-pinane-based ligands have been synthesized from (−)-α-pinene. Mixed with [(COD)2Rh]+[BF4]−, these ligands displayed moderate up to high catalytic activity in hydrogenation of dimethyl itaconate with dihydrogen. It has been observed that the structure of the ligand, the reaction temperature and solvent are important to define productivity of the phosphinite-based Rh-catalysts. Bisphosphinite ligands in hydrogenation reactions suffered from an Arbuzov rearrangement, leading to fast deactivation of the hydrogenation catalyst. In contrast, monophosphinite-derived Rh-catalysts showed increased productivity as well as thermal stability. An almost quantitative conversion of dimethyl itaconate has been achieved at elevated temperatures in toluene. Alternatively, hydrogenation of dimethyl itaconate with monophosphinite ligands has been carried out in MeOH at room temperature or 40°C and has led to a nearly quantitative conversion.

Hydrogen and/or syngas from steam reforming of glycerol. Study of platinum catalysts

In the present work, Pt catalysts prepared on different supports were evaluated in order to apply them in the steam reforming of glycerol reaction to obtain hydrogen and/or synthesis gas at temperatures lower than 450 °C. A strong support effect on the behavior of catalysts was determined. The presence of intermediate products allowed to propose a scheme of reactions that would explain the results obtained at different space times and temperatures studied. Materials with acid properties demonstrated low activity to gaseous products, with formation of lateral products due to dehydration and condensation reactions, which would lead to coke formation and to a fast catalyst deactivation. On the contrary, the catalyst prepared with a support with neutral properties permitted to obtain a catalyst with excellent activity levels to gaseous products, high selectivity to H 2, and a very well stability in time.

Counteracting Catalyst Deactivation in Methane Aromatization with a Two Zone Fluidized Bed Reactor

Methane aromatization is a promising alternative for the transformation of natural gas to liquid products but suffers the problem of a fast catalyst deactivation. The use of a two zone fluidized bed reactor (TZFBR) has been studied as a method to counteract this problem. In this reactor, two zones are created in a fluid bed by feeding the hydrocarbon at an intermediate point and a regenerating gas to the bottom of the reactor. A suitable catalyst for operation in the fluid bed has been developed. The results show that the TZFBR provides stable operation, thanks to the in situ regeneration of the catalyst in the lower part of the reactor. Three regenerating agents have been tested: oxygen, water, and carbon dioxide. Steady state operation has been achieved with all of them, but the best selectivity to aromatic products (benzene, toluene, and xylenes) was obtained with carbon dioxide. A significant effect of the reactor shape was also observed. The conversion and selectivity achieved with this reactor appear among the best values reported in the literature, with the advantage of being obtained at a steady state.

Structured catalyst supports and catalysts for the methane indirect internal steam reforming in the intermediate temperature SOFC

Open cell metal foams made from Ni, Fe–Cr steel and Ni–Al intermetallic were studied as candidate catalyst supports for the internal indirect methane steam reforming. All the samples exhibited good corrosive resistance during 500–1000 h testing in H 2–H 2O–Ar environment at 600 °C. NiO/8YSZ composite based catalysts doped with fluorite-like (Pr 0.3Ce 0.35Zr 0.35O 2) or perovskite-like (La 0.8Pr 0.2Mn 0.2Cr 0.8O 3) complex oxides with high lattice oxygen mobility and promoted with Pt or Ru were prepared and deposited on the foam-structure supports. Both good catalyst adhesion and stable catalyst performance were achieved in the case of the Ni–Al foam supported catalysts. The Fe–Cr support reacted with the catalytic active components resulting in fast catalyst deactivation. The foam supported catalyst performance was compared with the same catalyst prepared in a form of 0.25 mm fraction. Porous supports with different porosities were prepared by the metal foam deformation and the catalyst performance depending on the support porosity (75–95%) was studied.

Nickel catalysts applied in steam reforming of glycerol for hydrogen production

Abstract In order to study catalysts to obtain hydrogen by steam reforming of glycerol, nickel catalysts supported on commercial α-Al 2 O 3 and α-Al 2 O 3 modified by addition of ZrO 2 and CeO 2 were prepared and characterized. Results show the support effect on stability of catalysts in this reaction carried out at atmospheric pressure and in the range 450–600 °C. The most stable system resulted to be Ni/CeO 2 /α-Al 2 O 3 . Results can be explained due to the Ce effect in inhibition of secondary dehydration reactions forming unsaturated hydrocarbons that are coke precursors generating fast catalyst deactivation.

Solid acid alkylation of isobutane by butenes: the path from the ascertainment of the reasons for fast deactivation to the technological execution of the process

A short review of solid acid alkylation processes; the conception of the mechanism of goal and side conversion of isobutane and butenes, the deactivation nature of catalysts being used, and the possibility for their reactivation and industrial application is given. It was demonstrated that hydride transfer from isobutane molecules is the key process under which the catalytic cycles of alkylation retain and saturated hydrocarbons are formed as the process products. The main reason for the deactivation of alkylation catalysts is the formation of alkylcyclopentadienes and related compounds belonging to butenes. The problems of the fast deactivation of solid alkylation catalysts are substantially solved by the organization of catalyst performance in the connected reaction-regeneration system and in the application of hydrogenation and extraction procedures of activity regeneration, for which hydrogen and initial isobutane are used. Many companies incline to this kind of organizing of uninterrupted solid acid alkylation, which is an alternate to liquid acid alkylation.

Catalytic Vapor Decomposition of Methane over Nickle Catalyst: Growth Rate and the Corresponding Microstructures of Carbon Nanofibers

Time-resolved intrinsic reaction rate of catalytic vapor deposition of methane into carbon nanofibers (CNFs) and hydrogen on supported Ni catalysts was determined under different reaction temperatures (773–973 K) and feed compositions (PH2 = 0–0.29 atm, PCH4 = 0:28–0.71 atm) and the microstructure of the produced CNFs was characterized by Raman and TEM. The results showed that, increasing the reaction temperature, methane partial pressure and decreasing hydrogen partial pressure increased the initial reaction rate but generally led to fast catalyst deactivation. A high carbon yield per unit catalyst was obtained as a compromise between initial reaction rate and catalyst deactivation rate. The microstructures of the produced CNFs had a close relationship with the initial reaction rate. The CNFs produced with high initial rate tended to have a small angle between the graphene layers and the growth axis, thin diameter and a hollow core. This phenomenon can be used for monitoring and controlling the CNFs synthesis process.