Research

19 pages, 6021 KiB

Open AccessArticle

Toluene Steam Reforming over Ni/CeZrO₂—The Influence of Steam to Carbon Ratio and Contact Time on the Catalyst Performance and Carbon Deposition

by Agata Łamacz

Catalysts 2022, 12(2), 219; https://0-doi-org.brum.beds.ac.uk/10.3390/catal12020219 - 15 Feb 2022

Cited by 5 | Viewed by 2394

Abstract

The formation of tars during coal or biomass gasification is a serious issue resulting in decreasing efficiency of the process and increased maintenance costs. The decomposition of tars can be conducted via catalytic steam reforming that enriches the produced gas in hydrogen. Nevertheless, [...] Read more.

The formation of tars during coal or biomass gasification is a serious issue resulting in decreasing efficiency of the process and increased maintenance costs. The decomposition of tars can be conducted via catalytic steam reforming that enriches the produced gas in hydrogen. Nevertheless, the catalyst should be characterized by high activity, stability, and resistance towards carbon deposition. Ceria-zirconia supported nickel (Ni/CeZrO₂) is a very good candidate to catalyze tar removal—Ni is an active phase for reforming reactions, while CeZrO₂ provides the active sites that play important roles in protecting the catalyst from carbon deposition. Ni/CeZrO₂ shows high activity in the steam reforming of model tar compounds. In this paper, its performance in the steam reforming of toluene and carbon deposition is discussed considering the changing parameters of the reaction: the temperature, steam to carbon ratio, and the contact time. Full article

(This article belongs to the Special Issue Catalysts in Environmental and Climate Protection)

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23 pages, 37930 KiB

Open AccessFeature PaperArticle

Extremely Stable and Durable Mixed Fe–Mn Oxides Supported on ZrO₂ for Practical Utilization in CLOU and CLC Processes

by Ewelina Ksepko and Rafal Lysowski

Catalysts 2021, 11(11), 1285; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111285 - 25 Oct 2021

Cited by 5 | Viewed by 1490

Abstract

This paper contains the results of research on a promising combustion technology known as chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU). The remarkable advantages of CLC are, among others, that concentrated CO₂ stream can be obtained after water [...] Read more.

This paper contains the results of research on a promising combustion technology known as chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU). The remarkable advantages of CLC are, among others, that concentrated CO₂ stream can be obtained after water condensation without any energy penalty for its separation or significant decrease of NO_x emissions. The objective of this work was to prepare a novel bi-metallic Fe–Mn supported on ZrO₂ oxygen carriers. Performance of these carriers for the CLOU and CLC process with nitrogen/air and hard coal/air was evaluated. One-cycle CLC tests were conducted with supported Fe–Mn oxygen carriers in thermogravimetric analyzer utilizing hard coal as a fuel. The effects of the oxygen carrier chemical composition and process temperature on the reaction rates were determined. Our study proved that for CLOU, properties formation of bixbyite and spinel forms are responsible. Among iron ferrites, we concluded that iron-rich compounds such as Fe₂MnO₄ over FeMn₂O₄ spinel type oxides are more effective for CLOU applications. Full article

(This article belongs to the Special Issue Catalysts in Environmental and Climate Protection)

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22 pages, 12855 KiB

Open AccessArticle

Stable Mixed Fe-Mn Oxides Supported on ZrO₂ Oxygen Carriers for Practical Utilization in CLC Processes

by Ewelina Ksepko and Rafal Lysowski

Catalysts 2021, 11(9), 1047; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11091047 - 29 Aug 2021

Cited by 7 | Viewed by 1711

Abstract

The objective of the research was to prepare Fe-based materials for use as oxygen carriers (OCs) and investigate their reactivity in terms of their applicability to energy systems. The performance of ZrO₂ supported Fe-Mn oxide oxygen carriers with hydrogen/air in an innovative [...] Read more.

The objective of the research was to prepare Fe-based materials for use as oxygen carriers (OCs) and investigate their reactivity in terms of their applicability to energy systems. The performance of ZrO₂ supported Fe-Mn oxide oxygen carriers with hydrogen/air in an innovative combustion technology known as chemical looping combustion (CLC) was analyzed. The influence of manganese addition (15–30 wt.%) on reactivity and other physical properties of oxygen carriers was discussed. Thermogravimetric analyses (TGA) were conducted to evaluate their performance. Multi-cycle tests were conducted in TGA with oxygen carriers utilizing gaseous fuel. The effect of redox cycle number and temperature on stability and oxygen transport capacity and redox reaction rate were also evaluated. Physical-chemical analysis such as phase composition was investigated by XRD, while morphology by SEM-EDS and surface area analyses were investigated by the BET method. For screening purposes, the reduction and oxidation were carried out from 800 °C to 1000 °C. Three-cycle TGA tests at the selected temperature range indicated that all novel oxygen carriers exhibited stable chemical looping combustion performance, apart from the reference material, i.e., Fe/Zr oxide. A stable reactivity of bimetallic OCs, together with complete H₂ combustion without signs of FeMn/Zr oxide agglomeration, were proved. Oxidation reaction was significantly faster than the reduction reaction for all oxygen carriers. Furthermore, the obtained data indicated that the materials have a low cost of production, with superior reactivity towards hydrogen and air, making them perfect matching carriers for industrial applications for power generation. Full article

(This article belongs to the Special Issue Catalysts in Environmental and Climate Protection)

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21 pages, 5587 KiB

Open AccessFeature PaperArticle

SO₂ Poisoning and Recovery of Copper-Based Activated Carbon Catalysts for Selective Catalytic Reduction of NO with NH₃ at Low Temperature

by Marwa Saad, Agnieszka Szymaszek, Anna Białas, Bogdan Samojeden and Monika Motak

Catalysts 2020, 10(12), 1426; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10121426 - 05 Dec 2020

Cited by 3 | Viewed by 2513

Abstract

A series of materials based on activated carbon (AC) with copper deposited in various amounts were prepared using an incipient wetness impregnation method and tested as catalysts for selective catalytic reduction of nitrogen oxides with ammonia. The samples were poisoned with SO₂ [...] Read more.

A series of materials based on activated carbon (AC) with copper deposited in various amounts were prepared using an incipient wetness impregnation method and tested as catalysts for selective catalytic reduction of nitrogen oxides with ammonia. The samples were poisoned with SO₂ and regenerated in order to analyze their susceptibility to deactivation by the harmful component of exhaust gas. NO conversion over the fresh catalyst doped with 10 wt.% of Cu reached 81% of NO conversion at 140 °C and about 90% in the temperature range of 260–300 °C. The rate of poisoning with SO₂ was dependent on Cu loading, but in general, it lowered NO conversion due to the formation of (NH₄)₂SO₄ deposits that blocked the active sites of the catalysts. After regeneration, the catalytic activity of the materials was restored and NO conversion exceeded 70% for all of the samples. Full article

(This article belongs to the Special Issue Catalysts in Environmental and Climate Protection)

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20 pages, 3334 KiB

Open AccessFeature PaperArticle

The Enhanced Performance of N-Modified Activated Carbon Promoted with Ce in Selective Catalytic Reduction of NOx with NH₃

by Marwa Saad, Agnieszka Szymaszek, Anna Białas, Bogdan Samojeden and Monika Motak

Catalysts 2020, 10(12), 1423; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10121423 - 05 Dec 2020

Cited by 8 | Viewed by 2478

Abstract

The goal of the study was to modify activated carbon (AC) with nitrogen groups and ceria and to test the obtained materials in low temperature selective catalytic reduction of nitrogen oxides. For that purpose, the starting AC was oxidized with HNO₃ of [...] Read more.

The goal of the study was to modify activated carbon (AC) with nitrogen groups and ceria and to test the obtained materials in low temperature selective catalytic reduction of nitrogen oxides. For that purpose, the starting AC was oxidized with HNO₃ of various concentrations, modified with urea and doped with 0.5 wt.% of Ce. It was observed that the increased concentration of acid influenced the catalytic activity, since textural and surface chemistry of activated carbon was changed. The most active sample was that modified with 14 M HNO₃ and it reached 96% of NO conversion at 300 °C. Additionally, the addition of Ce improved the catalytic performance of modified AC, and NO was reduced according to oxidation–reduction mechanism, characteristic for supported metal oxides. Nevertheless, the samples promoted with Ce emitted significantly higher amount of CO₂ comparing to the non-promoted ones. Full article

(This article belongs to the Special Issue Catalysts in Environmental and Climate Protection)

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14 pages, 1575 KiB

Open AccessArticle

On Catalytic Behavior of Bulk Mo₂C in the Hydrodenitrogenation of Indole over a Wide Range of Conversion Thereof

by Marek Lewandowski, Rafał Janus, Mariusz Wądrzyk, Agnieszka Szymańska-Kolasa, Céline Sayag and Gérald Djéga-Mariadassou

Catalysts 2020, 10(11), 1355; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10111355 - 21 Nov 2020

Cited by 5 | Viewed by 2125

Abstract

The catalytic activity of bulk molybdenum carbide (Mo₂C) in the hydrodenitrogenation (HDN) of indole was studied. The catalyst was synthesized using a temperature-programmed reaction of the respective oxide precursor (MoO₃) with the carburizing gas mixture of 10 vol.\% CH [...] Read more.

The catalytic activity of bulk molybdenum carbide (Mo₂C) in the hydrodenitrogenation (HDN) of indole was studied. The catalyst was synthesized using a temperature-programmed reaction of the respective oxide precursor (MoO₃) with the carburizing gas mixture of 10 vol.\% CH₄/H₂. The resultant material was characterized using X-ray diffraction, CO chemisorption, and nitrogen adsorption. The catalytic activity was studied in the HDN of indole over a wide range of conversion thereof and in the presence of a low amount of sulfur (50 ppm), which was used to simulate the processing of real petroleum intermediates. The molybdenum carbide has shown high activity under the tested operating conditions. Apparently, the bulk molybdenum carbide turned out to be selective towards the formation of aromatic products such as ethylbenzene, toluene, and benzene. The main products of HDN were ethylbenzene and ethylcyclohexane. After 99% conversion of indole HDN was reached (i.e., lack of N-containing compounds in the products was observed), the hydrogenation of ethylbenzene to ethylcyclohexane took place. Thus, the catalytic behavior of bulk molybdenum carbide for the HDN of indole is completely different compared to previously studied sulfide-based systems. Full article

(This article belongs to the Special Issue Catalysts in Environmental and Climate Protection)

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11 pages, 3944 KiB

Open AccessArticle

Deactivation Effect of CaO on Mn-Ce/AC Catalyst for SCR of NO with NH₃ at Low Temperature

by Zenghui Su, Shan Ren, Zhichao Chen, Jie Yang, Yuhan Zhou, Lijun Jiang and Chen Yang

Catalysts 2020, 10(8), 873; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10080873 - 04 Aug 2020

Cited by 12 | Viewed by 2363

Abstract

In this study, the poisoning effect of CaO on activated carbon (AC)-based Mn-Ce catalysts was discussed. Loading CaO inhibited the catalytic activity of the catalyst and the NO conversion of the catalyst decreased from 69.5% to 38.2% at 75 °C. The amount of [...] Read more.

In this study, the poisoning effect of CaO on activated carbon (AC)-based Mn-Ce catalysts was discussed. Loading CaO inhibited the catalytic activity of the catalyst and the NO conversion of the catalyst decreased from 69.5% to 38.2% at 75 °C. The amount of MnO₂ in AC surface decreased in the process of loading CaO, which was detrimental to the Selective Catalytic Reduction (SCR) performance of the catalyst. The change of manganese oxide form inhibited generation rate for the chemisorption oxygen and NO₂, which was the most critical reason for the decrease of catalytic activity. Besides, loaded CaO entered into the pores of the catalyst, which led to the blockage of the pores and further resulted in the decrease of the Brunauer-Emmett-Teller (BET) surface area and total pore volume. It also destroyed the oxygen-containing functional groups and acid site on the surface of AC. All of these caused the deactivation of Mn-Ce/AC catalyst after loading CaO. Full article

(This article belongs to the Special Issue Catalysts in Environmental and Climate Protection)

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12 pages, 3477 KiB

Open AccessArticle

Three-Dimensional Mesoporous Ni-CeO₂ Catalysts with Ni Embedded in the Pore Walls for CO₂ Methanation

by Luhui Wang, Junang Hu, Hui Liu, Qinhong Wei, Dandan Gong, Liuye Mo, Hengcong Tao and Chengyang Zhang

Catalysts 2020, 10(5), 523; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10050523 - 08 May 2020

Cited by 21 | Viewed by 3525

Abstract

Mesoporous Ni-based catalysts with Ni confined in nanochannels are widely used in CO₂ methanation. However, when Ni loadings are high, the nanochannels are easily blocked by nickel particles, which reduces the catalytic performance. In this work, three-dimensional mesoporous Ni-CeO₂-CSC catalysts [...] Read more.

Mesoporous Ni-based catalysts with Ni confined in nanochannels are widely used in CO₂ methanation. However, when Ni loadings are high, the nanochannels are easily blocked by nickel particles, which reduces the catalytic performance. In this work, three-dimensional mesoporous Ni-CeO₂-CSC catalysts with high Ni loadings (20−80 wt %) were prepared using a colloidal solution combustion method, and characterized by nitrogen adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and H₂ temperature programmed reduction (H₂-TPR). Among the catalysts with different Ni loadings, the 50% Ni-CeO₂-CSC with 50 wt % Ni loading exhibited the best catalytic performance in CO₂ methanation. Furthermore, the 50% Ni-CeO₂-CSC catalyst was stable for 50 h at 300° and 350 °C in CO₂ methanation. The characterization results illustrate that the 50% Ni-CeO₂-CSC catalyst has Ni particles smaller than 5 nm embedded in the pore walls, and the Ni particles interact with CeO₂. On the contrary, the 50% Ni-CeO₂-CP catalyst, prepared using the traditional coprecipitation method, is less active and selective for CO₂ methanation due to the larger size of the Ni and CeO₂ particles. The special three-dimensional mesoporous embedded structure in the 50% Ni-CeO₂-CSC can provide more metal–oxide interface and stabilize small Ni particles in pore walls, which makes the catalyst more active and stable in CO₂ methanation. Full article

(This article belongs to the Special Issue Catalysts in Environmental and Climate Protection)

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