Catalysts

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3 pages, 189 KiB

Open AccessEditorial

Catalyst Deactivation, Poisoning and Regeneration

by Stefano Cimino and Luciana Lisi

Catalysts 2019, 9(8), 668; https://doi.org/10.3390/catal9080668 - 5 Aug 2019

Cited by 18 | Viewed by 4431

Abstract

Catalyst life-time represents one of the most crucial economic aspects in most industrial catalytic processes, due to costly shut-downs, catalyst replacements and proper disposal of spent materials [...] Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

Research

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13 pages, 4396 KiB

Open AccessArticle

Thermal Deactivation of Rh/α-Al₂O₃ in the Catalytic Partial Oxidation of Iso-Octane: Effect of Flow Rate

by Roberto Batista, Andrea Carrera, Alessandra Beretta and Gianpiero Groppi

Catalysts 2019, 9(6), 532; https://doi.org/10.3390/catal9060532 - 14 Jun 2019

Cited by 13 | Viewed by 3360

Abstract

Catalytic partial oxidation (CPO) of logistic fuels is a promising technology for the small-scale and on-board production of syngas (H₂ and CO). Rh coated monoliths can be used as catalysts that, due to Rh high activity, allow the use of reduced reactor [...] Read more.

Catalytic partial oxidation (CPO) of logistic fuels is a promising technology for the small-scale and on-board production of syngas (H₂ and CO). Rh coated monoliths can be used as catalysts that, due to Rh high activity, allow the use of reduced reactor volumes (with contact time in the order of milliseconds) and the achievement of high syngas yield. As the CPO process is globally exothermic, it can be operated in adiabatic reactors. The reaction mechanism of the CPO process involves the superposition of exothermic and endothermic reactions at the catalyst inlet. Thus, a hot spot temperature is formed, which may lead to catalyst deactivation via sintering. In this work, the effect of the flow rate on the overall performance of a CPO-reformer has been studied, using iso-octane as model fuel. The focus has been on thermal behavior. The experimental investigation consisted of iC8-CPO tests at varying total flow rates from 5 to 15 NL/min, wherein axially resolved temperature and composition measurements were performed. The increase of flow rate resulted in a progressive increase of the hot spot temperature, with partial loss of activity in the entry zone of the monolith (as evidenced by repeated reference tests of CH₄-CPO); conversely, the adiabatic character of the reformer improved. A detailed modelling analysis provided the means for the interpretation of the observed results. The temperature hot spot can be limited by acting on the operating conditions of the process. However, a tradeoff is required between the stability of the catalyst and the achievement of high performances (syngas yield, reactants conversion, and reactor adiabaticity). Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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17 pages, 7279 KiB

Open AccessArticle

Catalytic Behaviour of Ce-Doped Ni Systems Supported on Stabilized Zirconia under Dry Reforming Conditions

by Ahmed Sadeq Al-Fatesh, Yasir Arafat, Ahmed Aidid Ibrahim, Samsudeen Olajide Kasim, Abdulrahman Alharthi, Anis Hamza Fakeeha, Ahmed Elhag Abasaeed, Giuseppe Bonura and Francesco Frusteri

Catalysts 2019, 9(5), 473; https://doi.org/10.3390/catal9050473 - 22 May 2019

Cited by 28 | Viewed by 4494

Abstract

Ni supported on bare and modified ZrO₂ samples were synthesized using the incipient wet impregnation method. The t-ZrO₂ phase was stabilized by incorporation of La₂O₃ into ZrO₂. Moreover, the influence of CeO₂-doping on [...] Read more.

Ni supported on bare and modified ZrO₂ samples were synthesized using the incipient wet impregnation method. The t-ZrO₂ phase was stabilized by incorporation of La₂O₃ into ZrO₂. Moreover, the influence of CeO₂-doping on the physico-chemical and catalytic properties under CO₂ reforming conditions was probed. The characterization data of the investigated catalysts were obtained by using XRD, CO₂/H₂-TPD, BET, TPR, TPO, TGA, XPS and TEM characterization techniques. In the pristine Ni/Zr catalyst, the t-ZrO₂ phase transformed into the monoclinic phase. However, upon support modification by La₂O₃, significant effects on the physicochemical properties were observed due to the monoclinic-to-tetragonal ZrO₂ phase transformation also affecting the catalytic activity. As a result, superior activity on the La₂O₃ modified Ni/Zr catalyst was achieved, while no relevant change in the surface properties and activity of the catalysts was detected after doping by CeO₂. The peculiar behavior of the Ni/La-ZrO₂ sample was related to higher dispersion of the active phase, with a more pronounced stabilization of the t-ZrO₂ phase. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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16 pages, 2520 KiB

Open AccessArticle

A Case Study for the Deactivation and Regeneration of a V₂O₅-WO₃/TiO₂ Catalyst in a Tail-End SCR Unit of a Municipal Waste Incineration Plant

by Stefano Cimino, Claudio Ferone, Raffaele Cioffi, Giovanni Perillo and Luciana Lisi

Catalysts 2019, 9(5), 464; https://doi.org/10.3390/catal9050464 - 20 May 2019

Cited by 18 | Viewed by 4865

Abstract

In this work, we set out to investigate the deactivation of a commercial V₂O₅-WO₃/TiO₂ monolith catalyst that operated for a total of 18,000 h in a selective catalytic reduction unit treating the exhaust gases of a [...] Read more.

In this work, we set out to investigate the deactivation of a commercial V₂O₅-WO₃/TiO₂ monolith catalyst that operated for a total of 18,000 h in a selective catalytic reduction unit treating the exhaust gases of a municipal waste incinerator in a tail end configuration. Extensive physical and chemical characterization analyses were performed comparing results for fresh and aged catalyst samples. The nature of poisoning species was determined with regards to their impact on the DeNOx catalytic activity which was experimentally evaluated through catalytic tests in the temperature range 90–500 °C at a gas hourly space velocity of 100,000 h⁻¹ (NO = NH₃ = 400 ppmv, 6% O₂). Two simple regeneration strategies were also investigated: thermal treatment under static air at 400–450 °C and water washing at room temperature. The effectiveness of each treatment was determined on the basis of its ability to remove specific poisoning compounds and to restore the original performance of the virgin catalyst. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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15 pages, 5021 KiB

Open AccessArticle

Deactivation of Commercial, High-Load o-Xylene Feed VO_x/TiO₂ Phthalic Anhydride Catalyst by Unusual Over-Reduction

by Oliver Richter and Gerhard Mestl

Catalysts 2019, 9(5), 435; https://doi.org/10.3390/catal9050435 - 9 May 2019

Cited by 8 | Viewed by 4556

Abstract

An unusual temporal behavior of the by-product spectrum, as well as the temperature profiles of a commercial phthalic anhydride reactor, indicated a non-typical change of the incumbent catalyst. In order to understand these observations, catalyst samples were taken from this reactor and analyzed [...] Read more.

An unusual temporal behavior of the by-product spectrum, as well as the temperature profiles of a commercial phthalic anhydride reactor, indicated a non-typical change of the incumbent catalyst. In order to understand these observations, catalyst samples were taken from this reactor and analyzed by standard physico-chemical methods. Catalyst samples from another commercial reference reactor with most similar operating conditions and catalyst lifetime were also taken for comparison. The detailed physical analysis did not indicate unusual thermal stress leading to catalyst deactivation by rutilisation or sintering of the titania phase. The chemical analysis did not reveal significant amounts of any of the known catalyst poisons, which would also contribute to an untypical catalyst deactivation/behavior. Quantitative X-ray diffraction measurements on the other hand revealed an unusually high degree of reduction of the vanadium species in the final polishing catalyst layer. Such an abnormal degree of catalyst reduction, and hence, irreversible damaging, was concluded to likely originate from a unit shutdown without sufficient air purging of the catalyst bed. Combustion analysis of the deactivated catalyst confirmed unusually high carbon contents in the finishing catalyst bed (L4) accompanied with a significant loss in the specific surface area by plugging the catalyst pores with high-molecular carbon deposits. According to the well-known Mars–van-Krevelen-mechanism, o-xylene and reaction intermediates remain adsorbed on the catalyst surface in case of a shutdown without air purging and will continue to consume lattice oxygen, accordingly reducing the catalytic species. This systematic investigation of used catalyst samples demonstrated the importance of sufficient air purging during and after a unit shutdown to avoid abnormal, irreversible damage and thus negative impact to catalyst performance. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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12 pages, 4277 KiB

Open AccessArticle

Decomposition of Al₂O₃-Supported PdSO₄ and Al₂(SO₄)₃ in the Regeneration of Methane Combustion Catalyst: A Model Catalyst Study

by Niko M. Kinnunen, Ville H. Nissinen, Janne T. Hirvi, Kauko Kallinen, Teuvo Maunula, Matthew Keenan and Mika Suvanto

Catalysts 2019, 9(5), 427; https://doi.org/10.3390/catal9050427 - 8 May 2019

Cited by 10 | Viewed by 5340

Abstract

Exhaust gas aftertreatment systems play a key role in controlling transportation greenhouse gas emissions. Modern aftertreatment systems, often based on Pd metal supported on aluminum oxide, provide high catalytic activity but are vulnerable to sulfur poisoning due to formation of inactive sulfate species. [...] Read more.

Exhaust gas aftertreatment systems play a key role in controlling transportation greenhouse gas emissions. Modern aftertreatment systems, often based on Pd metal supported on aluminum oxide, provide high catalytic activity but are vulnerable to sulfur poisoning due to formation of inactive sulfate species. This paper focuses on regeneration of Pd-based catalyst via the decomposition of alumina-supported aluminum and palladium sulfates existing both individually and in combination. Decomposition experiments were carried out under hydrogen (10% H₂/Ar), helium (He), low oxygen (0.1% O₂/He), and excess oxygen (10% O₂/He). The structure and composition of the model catalysts were examined before and after the decomposition reactions via powder X-ray diffraction and elemental sulfur analysis. The study revealed that individual alumina-supported aluminum sulfate decomposed at a higher temperature compared to individual alumina-supported palladium sulfate. The simultaneous presence of aluminum and palladium sulfates on the alumina support decreased their decomposition temperatures and led to a higher amount of metallic palladium than in the corresponding case of individual supported palladium sulfate. From a fundamental point of view, the lowest decomposition temperature was achieved in the presence of hydrogen gas, which is the optimal decomposition atmosphere among the studied conditions. In summary, aluminum sulfate has a two-fold role in the regeneration of a catalyst—it decreases the Pd sulfate decomposition temperature and hinders re-oxidation of less-active metallic palladium to active palladium oxide. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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10 pages, 2336 KiB

Open AccessArticle

Fundamentals of Sulfate Species in Methane Combustion Catalyst Operation and Regeneration—A Simulated Exhaust Gas Study

by Niko M. Kinnunen, Kauko Kallinen, Teuvo Maunula, Matthew Keenan and Mika Suvanto

Catalysts 2019, 9(5), 417; https://doi.org/10.3390/catal9050417 - 3 May 2019

Cited by 7 | Viewed by 3521

Abstract

Emission regulations and legislation inside the European Union (EU) have a target to reduce tailpipe emissions in the transportation sector. Exhaust gas aftertreatment systems play a key role in low emission vehicles, particularly when natural gas or bio-methane is used as the fuel. [...] Read more.

Emission regulations and legislation inside the European Union (EU) have a target to reduce tailpipe emissions in the transportation sector. Exhaust gas aftertreatment systems play a key role in low emission vehicles, particularly when natural gas or bio-methane is used as the fuel. The main question for methane operating vehicles is the durability of the palladium-rich aftertreatment system. To improve the durability of the catalysts, a regeneration method involving an efficient removal of sulfur species needs to be developed and implemented on the vehicle. This paper tackles the topic and its issues from a fundamental point of view. This study showed that Al₂(SO₄)₃ over Al₂O₃ support material inhibits re-oxidation of Pd to PdO, and thus hinders the formation of the low-temperature active phase, PdO_x. The presence of Al₂(SO₄)₃ increases light-off temperature, which may be due to a blocking of active sites. Overall, this study showed that research should also focus on support material development, not only active phase inspection. An active catalyst can always be developed, but the catalyst should have the ability to be regenerated. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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14 pages, 2302 KiB

Open AccessArticle

Dry Reforming of Methane over NiLa-Based Catalysts: Influence of Synthesis Method and Ba Addition on Catalytic Properties and Stability

by Ruan Gomes, Denilson Costa, Roberto Junior, Milena Santos, Cristiane Rodella, Roger Fréty, Alessandra Beretta and Soraia Brandão

Catalysts 2019, 9(4), 313; https://doi.org/10.3390/catal9040313 - 30 Mar 2019

Cited by 21 | Viewed by 4405

Abstract

CO₂ reforming of CH₄ to produce CO and H₂ is a traditional challenge in catalysis. This area is still very active because of the potentials offered by the combined utilization of two green-house gases. The development of active, stable, and [...] Read more.

CO₂ reforming of CH₄ to produce CO and H₂ is a traditional challenge in catalysis. This area is still very active because of the potentials offered by the combined utilization of two green-house gases. The development of active, stable, and economical catalysts remains a key factor for the exploitation of natural gas (NG) with captured CO₂ and biogas to produce chemicals or fuels via syngas. The major issue associated with the dry reforming process is catalyst deactivation by carbon deposition. The development of suitable catalyst formulations is one strategy for the mitigation of coking which becomes especially demanding when noble metal-free catalysts are targeted. In this work NiLa-based catalyst obtained from perovskite precursors La_1−xBa_xNiO₃ (x = 0.0; 0.05; 0.1 and 0.2) and NiO/La₂O₃ were synthesized, characterized by in situ and operando XRD and tested in the dry reforming of methane. The characterization results showed that the addition of barium promoted BaCO₃ segregation and changes in the catalyst structure. This partly affected the activity; however, the incorporation of Ba improved the catalyst resistance to deactivation process. The Ba-containing and Ba-free NiLa-based catalysts performed significantly better than NiO/La₂O₃ catalysts obtained by wet impregnation. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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16 pages, 3965 KiB

Open AccessArticle

Byproduct Analysis of SO₂ Poisoning on NH₃-SCR over MnFe/TiO₂ Catalysts at Medium to Low Temperatures

by Tsungyu Lee and Hsunling Bai

Catalysts 2019, 9(3), 265; https://doi.org/10.3390/catal9030265 - 15 Mar 2019

Cited by 12 | Viewed by 4069

Abstract

The byproducts of ammonia-selective catalytic reduction (NH₃-SCR) process over MnFe/TiO₂ catalysts under the conditions of both with and without SO₂ poisoning were analyzed. In addition to the NH₃-SCR reaction, the NH₃ oxidation and the NO oxidation [...] Read more.

The byproducts of ammonia-selective catalytic reduction (NH₃-SCR) process over MnFe/TiO₂ catalysts under the conditions of both with and without SO₂ poisoning were analyzed. In addition to the NH₃-SCR reaction, the NH₃ oxidation and the NO oxidation reactions were also evaluated at temperatures of 100–300 °C to clarify the reactions occurred during the SCR process. The results indicated that major byproducts for the NH₃ oxidation and NO oxidation tests were N₂O and NO₂, respectively, and their concentrations increased as the reaction temperature increased. For the NH₃-SCR test without the presence of SO₂, it revealed that N₂O was majorly from the NH₃-SCR reaction instead of from NH₃ oxidation reaction. The byproducts of N₂O and NO₂ for the NH₃-SCR reaction also increased after increasing the reaction temperature, which caused the decreasing of N₂-selectivity and NO consumption. For the NH₃-SCR test with SO₂ at 150 °C, there were two decay stages during SO₂ poisoning. The first decay was due to a certain amount of NH₃ preferably reacted with SO₂ instead of with NO or O₂. Then the catalysts were accumulated with metal sulfates and ammonium salts, which caused the second decay of NO conversion. The effluent N₂O increased as poisoning time increased, which was majorly from oxidation of unreacted NH₃. On the other hand, for the NH₃-SCR test with SO₂ at 300 °C, the NO conversion was not decreased after increasing the poisoning time, but the N₂O byproduct concentration was high. However, the SO₂ led to the formation of metal sulfates, which might inhibit NO oxidation reactions and cause the concentration of N₂O gradually decreased as well as the N₂-selectivity increased. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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15 pages, 3457 KiB

Open AccessFeature PaperArticle

Performance and Stability of Metal (Co, Mn, Cu)-Promoted La₂O₂SO₄ Oxygen Carrier for Chemical Looping Combustion of Methane

by Stefano Cimino, Gabriella Mancino and Luciana Lisi

Catalysts 2019, 9(2), 147; https://doi.org/10.3390/catal9020147 - 2 Feb 2019

Cited by 14 | Viewed by 3192

Abstract

Oxygen carrier materials based on La₂O₂SO₄ and promoted by small amounts (1% wt.) of transition metals, namely Co, Mn and Cu, have been synthesized and characterized by means of X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Temperature-programmed reduction/oxidation (TPR/TPO) and [...] Read more.

Oxygen carrier materials based on La₂O₂SO₄ and promoted by small amounts (1% wt.) of transition metals, namely Co, Mn and Cu, have been synthesized and characterized by means of X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Temperature-programmed reduction/oxidation (TPR/TPO) and thermogravimetry-mass-Fourier transform infrared spectrometry (TG-MS-FTIR) experiments under alternating feeds in order to investigate their potential use for the Chemical Looping Combustion process using either hydrogen or methane as the fuel. The chemical looping reactivity is based on the reversible redox cycle of sulfur from S⁶⁺ in La₂O₂SO₄ to S²⁻ in La₂O₂S and entails a large oxygen storage capacity, but it generally requires high temperatures to proceed, challenging material stability and durability. Herein we demonstrate a remarkable improvement of lattice oxygen availability and activity during the reduction step obtained by cost-effective metal doping in the order Co > Mn > Cu. Notably, the addition of Co or Mn has shown a significant beneficial effect to prevent the decomposition of the oxysulfate releasing SO₂, which is identified as the main cause of progressive deactivation for the unpromoted La₂O₂SO₄. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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15 pages, 11835 KiB

Open AccessArticle

Microstructural Characteristics of Vehicle-Aged Heavy-Duty Diesel Oxidation Catalyst and Natural Gas Three-Way Catalyst

by Tomi Kanerva, Mari Honkanen, Tanja Kolli, Olli Heikkinen, Kauko Kallinen, Tuomo Saarinen, Jouko Lahtinen, Eva Olsson, Riitta L. Keiski and Minnamari Vippola

Catalysts 2019, 9(2), 137; https://doi.org/10.3390/catal9020137 - 1 Feb 2019

Cited by 14 | Viewed by 4679

Abstract

Techniques to control vehicle engine emissions have been under increasing need for development during the last few years in the more and more strictly regulated society. In this study, vehicle-aged heavy-duty catalysts from diesel and natural gas engines were analyzed using a cross-sectional [...] Read more.

Techniques to control vehicle engine emissions have been under increasing need for development during the last few years in the more and more strictly regulated society. In this study, vehicle-aged heavy-duty catalysts from diesel and natural gas engines were analyzed using a cross-sectional electron microscopy method with both a scanning electron microscope and a transmission electron microscope. Also, additional supporting characterization methods including X-ray diffractometry, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and catalytic performance analyses were used to reveal the ageing effects. Structural and elemental investigations were performed on these samples, and the effect of real-life ageing of the catalyst was studied in comparison with fresh catalyst samples. In the real-life use of two different catalysts, the poison penetration varied greatly depending on the engine and fuel at hand: the diesel oxidation catalyst appeared to suffer more thorough changes than the natural gas catalyst, which was affected only in the inlet part of the catalyst. The most common poison, sulphur, in the diesel oxidation catalyst was connected to cerium-rich areas. On the other hand, the severities of the ageing effects were more pronounced in the natural gas catalyst, with heavy structural changes in the washcoat and high concentrations of poisons, mainly zinc, phosphorus and silicon, on the surface of the inlet part. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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10 pages, 4201 KiB

Open AccessArticle

In Situ Regeneration and Deactivation of Co-Zn/H-Beta Catalysts in Catalytic Reduction of NO_x with Propane

by Hua Pan, Dongmei Xu, Chi He and Chao Shen

Catalysts 2019, 9(1), 23; https://doi.org/10.3390/catal9010023 - 30 Dec 2018

Cited by 3 | Viewed by 3639

Abstract

Regeneration and deactivation behaviors of Co-Zn/H-Beta catalysts were investigated in NO_x reduction with C₃H₈. Co-Zn/H-Beta exhibited a good water resistance in the presence of 10 vol.% H₂O. However, there was a significant drop off in N [...] Read more.

Regeneration and deactivation behaviors of Co-Zn/H-Beta catalysts were investigated in NO_x reduction with C₃H₈. Co-Zn/H-Beta exhibited a good water resistance in the presence of 10 vol.% H₂O. However, there was a significant drop off in N₂ yield in the presence of SO₂. The formation of surface sulfate and coke decreased the surface area, blocked the pore structure, and reduced the availability of active sites of Co-Zn/H-Beta during the reaction of NO reduction by C₃H₈. The activity of catalyst regenerated by air oxidation followed by H₂ reduction was higher than that of catalyst regenerated by H₂ reduction followed by air oxidation. Among the catalysts regenerated by air oxidation followed by H₂ reduction with different regeneration temperatures, the optimal regeneration temperature was 550 °C. The textural properties of poisoned catalysts could be restored to the levels of fresh catalysts by the optimized regeneration process. The regeneration process of air oxidation followed by H₂ reduction could recover the active sites of cobalt and zinc species from sulfate species, as well as eliminate coke deposition on poisoned catalysts. The regeneration pathway of air oxidation followed by H₂ reduction is summarized as initial removal of coke by air oxidation and final reduction of the sulfate species by H₂. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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15 pages, 5112 KiB

Open AccessArticle

The Role of Impregnated Sodium Ions in Cu/SSZ-13 NH₃-SCR Catalysts

by Chen Wang, Jun Wang, Jianqiang Wang, Zhixin Wang, Zexiang Chen, Xiaolan Li, Meiqing Shen, Wenjun Yan and Xue Kang

Catalysts 2018, 8(12), 593; https://doi.org/10.3390/catal8120593 - 30 Nov 2018

Cited by 26 | Viewed by 4816

Abstract

To reveal the role of impregnated sodium (Na) ions in Cu/SSZ-13 catalysts, Cu/SSZ-13 catalysts with four Na-loading contents were prepared using an incipient wetness impregnation method and hydrothermally treated at 600 °C for 16 h. The physicochemical property and selective catalytic reduction (SCR) [...] Read more.

To reveal the role of impregnated sodium (Na) ions in Cu/SSZ-13 catalysts, Cu/SSZ-13 catalysts with four Na-loading contents were prepared using an incipient wetness impregnation method and hydrothermally treated at 600 °C for 16 h. The physicochemical property and selective catalytic reduction (SCR) activity of these catalysts were studied to probe the deactivation mechanism. The impregnated Na exists as Na⁺ on catalysts and results in the loss of both Brönsted acid sites and Cu²⁺ ions. Moreover, the high loading of Na ions destroy the framework structure of Cu/SSZ-13 and forms new phases (SiO₂/NaSiO₃ and amorphous species) when Na loading was higher than 1.0 mmol/g. The decreased Cu²⁺ ions finally transformed into Cu_xO, CuO, and CuAlO_x species. The inferior SCR activity of Na impregnated catalysts was mainly due to the reduced contents of Cu²⁺ ions at kinetic temperature region. The reduction in the amount of acid sites and Cu²⁺ ions, as well as copper oxide species (Cu_xO and CuO) formation, led to low SCR performance at high temperature. Our study also revealed that the existing problem of the Na ions’ effect should be well-considered, especially at high hydrothermal aging when diesel particulate filter (DPF) is applied in upstream of the SCR applications. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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16 pages, 3001 KiB

Open AccessArticle

Influence of Sulfur-Containing Sodium Salt Poisoned V₂O₅–WO₃/TiO₂ Catalysts on SO₂–SO₃ Conversion and NO Removal

by Haiping Xiao, Chaozong Dou, Hao Shi, Jinlin Ge and Li Cai

Catalysts 2018, 8(11), 541; https://doi.org/10.3390/catal8110541 - 13 Nov 2018

Cited by 12 | Viewed by 4747

Abstract

A series of poisoned catalysts with various forms and contents of sodium salts (Na₂SO₄ and Na₂S₂O₇) were prepared using the wet impregnation method. The influence of sodium salts poisoned catalysts on SO₂ oxidation [...] Read more.

A series of poisoned catalysts with various forms and contents of sodium salts (Na₂SO₄ and Na₂S₂O₇) were prepared using the wet impregnation method. The influence of sodium salts poisoned catalysts on SO₂ oxidation and NO reduction was investigated. The chemical and physical features of the catalysts were characterized via NH₃-temperature programmed desorption (NH₃-TPD), H₂-temperature programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FT-IR). The results showed that sodium salts poisoned catalysts led to a decrease in the denitration efficiency. The 3.6% Na₂SO₄ poisoned catalyst was the most severely deactivated with denitration efficiency of only 50.97% at 350 °C. The introduction of SO₄²⁻ and S₂O₇²⁻ created new Brønsted acid sites, which facilitated the adsorption of NH₃ and NO reduction. The sodium salts poisoned catalysts significantly increased the conversion of SO₂–SO₃. 3.6%Na₂S₂O₇ poisoned catalyst had the strongest effect on SO₂ oxidation and the catalyst achieved a maximum SO₂–SO₃-conversion of 1.44% at 410 °C. Characterization results showed sodium salts poisoned catalysts consumed the active ingredient and lowered the V⁴⁺/V⁵⁺ ratio, which suppressed catalytic performance. However, they increased the content of chemically adsorbed oxygen and the strength of V⁵⁺=O bonds, which promoted SO₂ oxidation. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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12 pages, 6191 KiB

Open AccessArticle

Water: Friend or Foe in Catalytic Hydrogenation? A Case Study Using Copper Catalysts

by Alisa Govender, Abdul S. Mahomed and Holger B. Friedrich

Catalysts 2018, 8(10), 474; https://doi.org/10.3390/catal8100474 - 19 Oct 2018

Cited by 7 | Viewed by 3539

Abstract

Copper oxide supported on alumina and copper chromite were synthesized, characterized, and subsequently tested for their catalytic activity toward the hydrogenation of octanal. Thereafter, the impact of water addition on the conversion and selectivity of the catalysts were investigated. The fresh catalysts were [...] Read more.

Copper oxide supported on alumina and copper chromite were synthesized, characterized, and subsequently tested for their catalytic activity toward the hydrogenation of octanal. Thereafter, the impact of water addition on the conversion and selectivity of the catalysts were investigated. The fresh catalysts were characterized using X-ray diffraction (XRD), BET surface area and pore volume, SEM, TEM, TGA-DSC, ICP, TPR, and TPD. An initial catalytic testing study was carried out using the catalysts to optimize the temperature and the hydrogen-to-aldehyde ratio—which were found to be 160 °C and 2, respectively—to obtain the best conversion and selectivity to octanol prior to water addition. Water impact studies were carried out under the same conditions. The copper chromite catalyst showed no deactivation or change in octanol selectivity when water was added to the feed. The alumina-supported catalyst showed no change in conversion, but the octanol selectivity improved marginally when water was added. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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Jump to: Editorial, Research

45 pages, 14361 KiB

Open AccessReview

Activation, Deactivation and Reversibility Phenomena in Homogeneous Catalysis: A Showcase Based on the Chemistry of Rhodium/Phosphine Catalysts

by Elisabetta Alberico, Saskia Möller, Moritz Horstmann, Hans-Joachim Drexler and Detlef Heller

Catalysts 2019, 9(7), 582; https://doi.org/10.3390/catal9070582 - 30 Jun 2019

Cited by 25 | Viewed by 9344

Abstract

In the present work, the rich chemistry of rhodium/phosphine complexes, which are applied as homogeneous catalysts to promote a wide range of chemical transformations, has been used to showcase how the in situ generation of precatalysts, the conversion of precatalysts into the actually [...] Read more.

In the present work, the rich chemistry of rhodium/phosphine complexes, which are applied as homogeneous catalysts to promote a wide range of chemical transformations, has been used to showcase how the in situ generation of precatalysts, the conversion of precatalysts into the actually active species, as well as the reaction of the catalyst itself with other components in the reaction medium (substrates, solvents, additives) can lead to a number of deactivation phenomena and thus impact the efficiency of a catalytic process. Such phenomena may go unnoticed or may be overlooked, thus preventing the full understanding of the catalytic process which is a prerequisite for its optimization. Based on recent findings both from others and the authors’ laboratory concerning the chemistry of rhodium/diphosphine complexes, some guidelines are provided for the optimal generation of the catalytic active species from a suitable rhodium precursor and the diphosphine of interest; for the choice of the best solvent to prevent aggregation of coordinatively unsaturated metal fragments and sequestration of the active metal through too strong metal–solvent interactions; for preventing catalyst poisoning due to irreversible reaction with the product of the catalytic process or impurities present in the substrate. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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