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17 pages, 7953 KiB

Open AccessArticle

Hard Template-Assisted Trans-Crystallization Synthesis of Hierarchically Porous Cu-SSZ-13 with Enhanced NH₃-SCR Performance

by Fuzhen Yang, Ying Xin, Xiaoli Zhu, Ahui Tang, Long Yu, Dongxu Han, Junxiu Jia, Yaning Lu and Zhaoliang Zhang

Catalysts 2023, 13(8), 1217; https://doi.org/10.3390/catal13081217 - 16 Aug 2023

Cited by 3 | Viewed by 1869

Abstract

Small porous Cu-SSZ-13 catalysts have recently been commercialized for the selective catalytic reduction of NO_x with ammonia (NH₃-SCR) on diesel vehicles. Unfortunately, the conventional Cu-SSZ-13 catalyst still confronts the challenge of diffusion limitations, which represent a major obstacle that reduces [...] Read more.

Small porous Cu-SSZ-13 catalysts have recently been commercialized for the selective catalytic reduction of NO_x with ammonia (NH₃-SCR) on diesel vehicles. Unfortunately, the conventional Cu-SSZ-13 catalyst still confronts the challenge of diffusion limitations, which represent a major obstacle that reduces the catalyst’s SCR performance. Herein, a hierarchically porous SSZ-13 zeolite was synthesized via a trans-crystallization method assisted by the use of carbon black as a hard template in a short synthetic period, and the corresponding Cu-SSZ-13 catalysts with mesopores exhibited improved low-temperature activity and hydrothermal stability when compared with their microporous counterpart. A series of characterizations revealed that the mesopores are conducive to an increase in Cu loading while helping to stabilize the CHA structure and maintain the Cu species in their ionic form. More importantly, intra-particle diffusion limitations are reduced via the introduction of the mesopores owing to the shortened diffusion path inside the SSZ-13 zeolite, thus not only enhancing the active sites’ accessibility but also promoting the diffusion of the reactants and products. This work contributes to the design and synthesis of a high-performance Cu-SSZ-13 zeolite SCR catalyst for the removal of NO_x emitted from diesel vehicles. Full article

(This article belongs to the Special Issue Catalysts for Selective Catalytic Reduction (SCR) and Related Reactions)

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13 pages, 7252 KiB

Open AccessFeature PaperArticle

Revealing the Roles of Cu/Ba on Ce-Based Passive NO_x Adsorbers

by Mingming Pei, Yuxin Fan, Haidi Xu, Zhihua Lian, Wei Tan, Jianli Wang and Yaoqiang Chen

Catalysts 2023, 13(8), 1180; https://doi.org/10.3390/catal13081180 - 2 Aug 2023

Cited by 3 | Viewed by 1297

Abstract

At present, passive NO_x adsorbers (PNAs) represent one of the most effective technologies for addressing NO_x emissions from diesel engines during cold-start periods. Conventional PNAs, which primarily consist of noble metals (such as Pt, Pd, and Ag) loaded on metal oxides [...] Read more.

At present, passive NO_x adsorbers (PNAs) represent one of the most effective technologies for addressing NO_x emissions from diesel engines during cold-start periods. Conventional PNAs, which primarily consist of noble metals (such as Pt, Pd, and Ag) loaded on metal oxides or zeolites, share the common drawback of high production costs. Consequently, developing low-cost PNAs with outstanding NO_x storage performance remains a significant challenge. In this study, a series of CuxBa5Ce adsorbents were synthesized using the impregnation method, and a monolithic adsorbent was employed to evaluate NO_x storage and release performance. Techniques such as XRD, UV-Vis DRs, H₂-TPR, XPS, and in situ DRIFTs confirmed the crucial roles of Cu and Ba in NO_x storage and release. Specifically, the incorporation of Cu into CeO₂ enhanced NO_x storage performance. Moreover, in the Cu3Ba5Ce adsorbent, the addition of Ba not only introduced new storage sites and altered the stability of NO_x adsorption species but also helped prevent the aggregation of CuO, thereby prolonging the complete NO_x storage duration and satisfying desorption temperature requirements. The Cu3Ba5Ce adsorbent exhibited the most favorable NO_x storage performance, including a complete NO_x storage time of 135 s and a NO_x storage efficiency exceeding 50% at 80 °C over a 10 min period. While PNAs loaded with noble metals, such as Pd/CeO₂ and Pt/CeO₂, exhibited NO_x storage efficiencies below 50% after adsorbing for 5 min at 80 °C. Therefore, this research offered a crucial strategy for developing non-noble-metal-loaded, Ce-based PNAs. Full article

(This article belongs to the Special Issue Catalysts for Selective Catalytic Reduction (SCR) and Related Reactions)

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12 pages, 5175 KiB

Open AccessArticle

The Catalyst of Ruthenium Nanoparticles Decorated Silicalite-1 Zeolite for Boosting Catalytic Soot Oxidation

by Yuanfeng Li, Hao Guo, Jing Xiong, Yaxiao Ma, Xuanzhen Li, Peng Zhang, Sicheng Zhang and Yuechang Wei

Catalysts 2023, 13(8), 1167; https://doi.org/10.3390/catal13081167 - 30 Jul 2023

Cited by 5 | Viewed by 1515

Abstract

Herein, the Ruthenium nanoparticles (NPs) with the size of 12 nm were decorated on the hexagonal prism silicalite-1 (Ru/S-1) by the gas bubbling-assisted membrane reduction method (GBMR). The adsorption/activation properties are improved for reactant molecules due to the formation of an interfacial structure [...] Read more.

Herein, the Ruthenium nanoparticles (NPs) with the size of 12 nm were decorated on the hexagonal prism silicalite-1 (Ru/S-1) by the gas bubbling-assisted membrane reduction method (GBMR). The adsorption/activation properties are improved for reactant molecules due to the formation of an interfacial structure that enhances the interaction between the Ru NPs and S-1. The Ru/S-1 catalyst displays the highest catalytic activity (T₅₀ = 356 °C) and CO₂ selectivity (S_CO2^m = 99.9%). Moreover, no obvious deactivation was observed over the Ru/S-1 catalyst even after five cycles, and the values of T₅₀ and S_CO2^m after cycling five times are similar to the fresh catalyst. The Ru/S-1 catalyst with excellent catalytic performance can be compared with a series of noble metal catalysts for soot oxidation. The catalytic mechanism of the Ru/S-1 catalyst was revealed by in situ characterization for soot oxidation. The interfacial effect between Ru NPs and S-1 plays an important role in the conversion of NO to NO₂ during soot oxidation. Preparation of Ru/S-1 catalyst provides a hopeful way to obtain considerably low-cost and highly stable auto-exhaust treatment catalysts. Full article

(This article belongs to the Special Issue Catalysts for Selective Catalytic Reduction (SCR) and Related Reactions)

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13 pages, 7008 KiB

Open AccessFeature PaperArticle

A Comparative Study on the Effect of Surface and Bulk Sulfates on the High-Temperature Selective Catalytic Reduction of NO with NH₃ over CeO₂

by Chong Tan, Zhiwen Gu, Songil Sin, Jiawei Ji, Yan Wang, Baiyun Zhu, Lijun Cheng, Chunkai Huang, Lulu Li, Hongliang Zhang and Changjin Tang

Catalysts 2023, 13(8), 1162; https://doi.org/10.3390/catal13081162 - 28 Jul 2023

Cited by 3 | Viewed by 1100

Abstract

Herein, two CeO₂ samples dominantly decorated with surface and bulk sulfates were constructed and their distinct effects on high-temperature NH₃-SCR were investigated by strictly controlling the sulfate content at a comparable level. The obtainment of surface and bulk sulfates was [...] Read more.

Herein, two CeO₂ samples dominantly decorated with surface and bulk sulfates were constructed and their distinct effects on high-temperature NH₃-SCR were investigated by strictly controlling the sulfate content at a comparable level. The obtainment of surface and bulk sulfates was revealed using a designed leaching experiment, and further evidenced by the characterization results from XPS and H₂-TPR. In comparison with CeO₂ modified with bulk sulfates (B-CeS), sufficient acid sites with strong intensity were generated on CeO₂ modified with surface sulfates (S-CeS). In addition, due to electron-withdrawing effect from S=O in sulfate species, NH₃ oxidation over S-CeS was greatly suppressed, providing an additional contribution to enhanced performance in high-temperature NH₃-SCR. Full article

(This article belongs to the Special Issue Catalysts for Selective Catalytic Reduction (SCR) and Related Reactions)

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15 pages, 7877 KiB

Open AccessEditor’s ChoiceArticle

Engineering Surface Properties of CuO/Ce_0.6Zr_0.4O₂ Catalysts for Efficient Low-Temperature Toluene Oxidation

by Mingyue Wang, Qiulin Zhang, Meilin Zou, Jingge Wang, Danrui Zhu, Jiaying Liu, Junwei Wang, Yang Zuo, Jianjun Chen and Ping Ning

Catalysts 2023, 13(5), 866; https://doi.org/10.3390/catal13050866 - 10 May 2023

Cited by 2 | Viewed by 1510

Abstract

The development of superior low-temperature catalytic performance and inexpensive catalysts for the removal of volatile organic compounds (VOCs) is crucial for their industrial application. Herein, CuO/Ce_0.6Zr_0.4O₂ catalysts calcinated at different temperatures (Cu/CZ-X, X represented calcination temperature) were prepared [...] Read more.

The development of superior low-temperature catalytic performance and inexpensive catalysts for the removal of volatile organic compounds (VOCs) is crucial for their industrial application. Herein, CuO/Ce_0.6Zr_0.4O₂ catalysts calcinated at different temperatures (Cu/CZ-X, X represented calcination temperature) were prepared and used to eliminate toluene. It can be found that Cu/CZ-550 presented the highest low-temperature catalytic activity, with the lowest temperature (220 °C) 50% conversion of toluene, the highest normalized reaction rate (3.1 × 10⁻⁵ mol·g⁻¹·s⁻¹ at 180 °C) and the lowest apparent activation energy value (86.3 ± 4.7 kJ·mol⁻¹). Systematically, the surface properties analysis results showed that the optimum redox property, abundant oxygen vacancies, and plentiful surface Ce³⁺ species over Cu/CZ-550 were associated with the strong interaction between Cu and support could significantly favor the adsorption and activation of toluene, thus resulting in its superior catalytic performance. Full article

(This article belongs to the Special Issue Catalysts for Selective Catalytic Reduction (SCR) and Related Reactions)

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16 pages, 3619 KiB

Open AccessEditor’s ChoiceArticle

Cobalt-/pH-Modified V₂O₅-MoO₃/TiO₂ Catalyst with Enhanced Activity for the Low-Temperature Selective Catalytic Reduction Process

by Ruonan Wang, Yanli Zhang, Xing Fan and Jian Li

Catalysts 2023, 13(5), 844; https://doi.org/10.3390/catal13050844 - 6 May 2023

Cited by 5 | Viewed by 1685

Abstract

Currently, the elimination of gaseous pollutants—particularly nitrogen oxides—has emerged as a significant concern. Among various deNO_x technologies, selective catalytic reduction (SCR) has gained prominence as the primary approach for NO_x abatement, owing to its superior performance. In this study, novel low-temperature [...] Read more.

Currently, the elimination of gaseous pollutants—particularly nitrogen oxides—has emerged as a significant concern. Among various deNO_x technologies, selective catalytic reduction (SCR) has gained prominence as the primary approach for NO_x abatement, owing to its superior performance. In this study, novel low-temperature SCR catalysts were developed by regulating the pH value and doping cobalt based on a V₂O₅-MoO₃/TiO₂ (VMT) catalyst. The results show an increased SCR performance with 82.8% and 91.1% for catalysts after pH (=10) modification (VMT-10) and (1 wt%) Co/pH (=10) modification (1CoVMT-10), respectively. H₂-TPR, NH₃-TPD, XPS and DRIFTS confirmed that the pH regulation transformed polymerization V species into isolated V⁵⁺=O, thus leading to an increase in the number of acid sites, which enhanced the NH₃ and NO₂ adsorption capacity. Furthermore, the DRIFTS study indicated that the NH₃-SCR reaction over 1CoVMT-10 followed the E–R and L–H mechanism. Full article

(This article belongs to the Special Issue Catalysts for Selective Catalytic Reduction (SCR) and Related Reactions)

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15 pages, 4575 KiB

Open AccessArticle

Low-Temperature NH₃-SCR Performance and In Situ DRIFTS Study on Zeolite X-Supported Different Crystal Phases of MnO₂ Catalysts

by Lin Chen, Shan Ren, Tao Chen, Xiaodi Li, Mingming Wang, Zhichao Chen and Qingcai Liu

Catalysts 2023, 13(4), 682; https://doi.org/10.3390/catal13040682 - 31 Mar 2023

Viewed by 1625

Abstract

In this study, a series of zeolite-X-supported different crystal phases of MnO₂ (α-MnO₂, β-MnO₂, γ-MnO₂, and σ-MnO₂) catalysts were prepared via a solid-state diffusion method and high-heat treatment method to explore their low-temperature NH [...] Read more.

In this study, a series of zeolite-X-supported different crystal phases of MnO₂ (α-MnO₂, β-MnO₂, γ-MnO₂, and σ-MnO₂) catalysts were prepared via a solid-state diffusion method and high-heat treatment method to explore their low-temperature NH₃-SCR performance. All of the catalysts featured typical octahedral zeolite X structures and manganese dioxides species of various crystal types dispersed across the support surface. Throughout the entire temperature range of the reaction, γ-MnO₂/X catalyst had the highest NO conversion. Additionally, β-MnO₂/X, γ-MnO₂/X, and σ-MnO₂/X catalysts had nearly 100% of N₂ selectivity, whereas the α-MnO₂/X catalyst had the lowest N₂ selectivity (about 90%) below 125 °C. Moreover, the γ-MnO₂/X catalyst demonstrated superior acidity capacity and reduction ability compared with the other three catalysts. All the catalysts contained the essential intermediates NH₂NO and NH₄NO₃ species, which are essential to the SCR reaction. More acid sites and nitrate species existed on the γ-MnO₂/X catalyst than on the other catalysts, thereby boosting the SCR reaction. Full article

(This article belongs to the Special Issue Catalysts for Selective Catalytic Reduction (SCR) and Related Reactions)

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Review

Jump to: Research

23 pages, 3749 KiB

Open AccessFeature PaperReview

Research Progress on Metal Oxides for the Selective Catalytic Reduction of NO_x with Ammonia

by Lanyi Wang, Shengran Zhou, Mengxia You, Di Yu, Chunlei Zhang, Siyu Gao, Xuehua Yu and Zhen Zhao

Catalysts 2023, 13(7), 1086; https://doi.org/10.3390/catal13071086 - 11 Jul 2023

Cited by 6 | Viewed by 2455

Abstract

Nitrogen oxides emitted from diesel vehicle exhaust seriously endanger the atmospheric environment and human health, which have attracted people’s attention. Among numerous nitrogen oxide (NO_x) removal technologies, photocatalytic removal of NO_x and SCR have received widespread attention. The photocatalytic treatment [...] Read more.

Nitrogen oxides emitted from diesel vehicle exhaust seriously endanger the atmospheric environment and human health, which have attracted people’s attention. Among numerous nitrogen oxide (NO_x) removal technologies, photocatalytic removal of NO_x and SCR have received widespread attention. The photocatalytic treatment of NO_x technology is a good choice due to its mild reaction conditions and low costs. Moreover, NH₃-SCR has been widely used in denitration technology and plays an important role in controlling NO_x emissions. In NH₃-SCR technology, the development of high-efficiency catalysts is an important part. This paper summarizes the research progress of metal oxide catalysts for NH₃-SCR reactions, including V-based catalysts, Mn-based catalysts, Fe-based catalysts, Ce-based catalysts, and Cu-based catalysts. Meanwhile, the detailed process of the NH₃-SCR reaction was also introduced. In addition, this paper also describes a possible SO₂ poisoning mechanism and the stability of the catalysts. Finally, the problems and prospects of metal oxide catalysts for NO_x removal were also proposed. Full article

(This article belongs to the Special Issue Catalysts for Selective Catalytic Reduction (SCR) and Related Reactions)

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