Synthesis of High-Silica LTA and UFI Zeolites and NH<sub>3</sub>–SCR Performance of Their Copper-Exchanged Form

Jo, Donghui; Ryu, Taekyung; Park, Gi Tae; Kim, Pyung Soon; Kim, Chang Hwan; Nam, In−Sik; Hong, Suk Bong

doi:10.1021/acscatal.6b00489

Cited by 125 publications

(77 citation statements)

References 31 publications

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“…We also tested the deNO x activity of an over‐exchanged Cu‐LTA catalyst, that is, Cu‐LTA‐16‐0.65. While exhibiting similar activity after aging at 750 °C, as recently reported, it became almost zero when further aged at 900 °C, unlike the others with lower Cu/Al ratios (Figure a). This may be due to the easy formation of CuO x clusters in the over‐exchanged catalyst during hydrothermal treatment, which has a detrimental effect on the stability of the zeolite support.…”

Section: Figuresupporting

confidence: 85%

Fully Copper‐Exchanged High‐Silica LTA Zeolites as Unrivaled Hydrothermally Stable NH₃‐SCR Catalysts

et al. 2017

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Tighter CO2 emission standards from mobile sources are being legislated globally in order to address the concerns regarding anthropogenic climate change. Hence, automotive manufacturers have developed a variety of new propulsion systems, including battery electric, plug-in hybrid, and even fuel cell electric vehicles.[1] However, there is a general consensus that internal combustion engines will continue to dominate the market for the foreseeable future. [1,2] As such, fuel-efficient combustion technologies like diesel engines offer superior green-house gas reduction potential. One technical obstacle to broader diesel implementation is the required lean NOx aftertreatment system, especially to meet upcoming strict emission regulations. NOx is extremely difficult to reduce under an oxygen-rich environment.[3] Although its selective catalytic reduction by urea (urea-SCR) has recently been commercialized, the operation window of this technology is severely limited by the decomposition temperature (~ 200 °C) of urea into NH3 and by SCR catalyst deactivation at temperatures higher than 750 °C.[4]This prohibits closer placement of the catalyst to the engine, requiring an aggressive warm-up with extra fuel burning during the cold-start. Furthermore, when integrating a mandatory particulate filter in the modern diesel aftertreatment system to mitigate soot and ash, the frequent regeneration of diesel particulate filters is required before a certain accumulation of soot, resulting in large temperature spikes. Improvement of the thermal durability of the SCR catalysts would, therefore, be the key to maximizing the fuel efficiency, as well as to producing clean emissions from diesel engines. Metal-exchanged zeolites have drawn much attention as diesel vehicle SCR catalysts, and with copper-exchanged ZSM-5 and SSZ-13, which are medium-and small-pore zeolites with MFI and CHA topologies, respectively, [5] have been most widely studied for this reaction.[4] Cu-SSZ-13 has recently been implemented as the current standard catalyst in the mobile SCR technology because of its superior thermal durability compared to already known catalysts. When aged at 850 °C, however, even this catalyst, whose fresh form achieves greater than 90% NOx conversion at 250 -400 °C in steady state, loses its CHA structure and forms copper oxide (CuOx) species, leading to severe activity loss. [6] Although zeolite A (framework type LTA) is the first synthetic zeolite to be prepared, [7] its catalytic applications have long been severely restricted due to its poor thermal stability originating from the high framework Al content (Si/Al = 1.0). However, a recent success in the benzylimidazolium-mediated synthesis of its unprecedented high-silica (Si/Al > 8) form provides a key advantage in terms of structural stability with tunable loading of catalytically-active metal centers.[8] Here we report that when the copper ion exchange level increases to 100% (Cu/Al = 0.50), the high-silica (Si/Al = 16-23) Cu-LTA catalysts hydrothermally aged at 900 °C, i.e., t...

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Section: Figuresupporting

confidence: 85%

Fully Copper‐Exchanged High‐Silica LTA Zeolites as Unrivaled Hydrothermally Stable NH₃‐SCR Catalysts

et al. 2017

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“…Despite the great progress for the organic template-free synthesis of aluminosilicate FER zeolite, the obtained product is always Al-rich (Si/Al ratio no more than 10). Normally, high-silica aluminosilicate FER zeolites could be achieved with the assistance of organic templates [83][84][85][86]. In recent years, it was found that aluminosilicate FER zeolites with relatively high Si/Al ratio could be synthesized by adding zeolite seeds with different topologies from FER, which is regarded as a breakthrough for the synthesis of high silica FER zeolite [21,87].…”

Section: Organotemplate-free Synthesis Of Aluminosilicate Fer Zeolitementioning

confidence: 99%

Advances in the Synthesis of Ferrierite Zeolite

Zhu

et al. 2020

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As one of the most important porous materials, zeolites with intricate micropores have been widely employed as catalysts for decades due to their large pore volume, high surface area, and good thermal and hydrothermal stabilities. Among them, ferrierite (FER) zeolite with a two-dimensional micropore structure is an excellent heterogeneous catalyst for isomerization, carbonylation, cracking, and so on. In the past years, considering the important industrial application of FER zeolite, great efforts have been made to improve the synthesis of FER zeolite and thus decrease the synthesis cost and enhance catalytic performance. In this review, we briefly summarize the advances in the synthesis of FER zeolite including the development of synthesis routes, the use of organic templates, organotemplate-free synthesis, the strategies of morphology control, and the creation of intra-crystalline mesopores. Furthermore, the synthesis of hetero-atomic FER zeolites such as Fe-FER and Ti-FER has been discussed.

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“…Initially vanadia/titania systems [4] were considered the most -promising SCR catalysts, however, due to issues with hydrothermal durability and concerns over vanadia waste (particularly in the US), metal-exchanged zeolites became more widely studied and used in vehicle applications. Originally Cu/Fe ZSM-5 [5, 6] and Cu/Fe-beta [7, 8] were studied for NH 3 –SCR for deNOx, however, issues relating to thermal stability and degradation (caused by temperature spikes in the catalyst bed due to the combustion of unburned hydrocarbons) [9] motivated research in to the exploration of new, more stable systems including small-pore metal-exchanged zeolites, such as SSZ-13 (CHA) [10, 11], zeolite A (LTA) [12] and SSZ-39 (AEI) [13] for SCR applications. Cu–SSZ-13 is the subject of a considerable amount of research as it has both a higher activity, selectivity and is less susceptible to thermal degradation than ZSM-5 and beta based systems [14–16], chabazite is a small pore zeolite (maximum ring size 8 t-sites) composed of double 6 ring (d6r) and chabazite (cha) cages with the d6r cages in an AABBCC packing sequence (see Fig.…”

Section: Introductionmentioning

confidence: 99%

Operando Spectroscopic Studies of Cu–SSZ-13 for NH3–SCR deNOx Investigates the Role of NH3 in Observed Cu(II) Reduction at High NO Conversions

et al. 2018

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The small pore zeolite chabazite (SSZ-13) in the copper exchanged form is a very efficient material for the selective catalytic reduction by ammonia (NH 3 ) of nitrogen oxides (NOx) from the exhaust of lean burn engines, typically diesel powered vehicles. The full mechanism occurring during the NH 3 -SCR process is currently debated with outstanding questions including the nature and role of the catalytically active sites. Time-resolved operando spectroscopic techniques have been used to provide new level of insights in to the mechanism of NH 3 -SCR, to show that the origin of stable Cu(I) species under SCR conditions is potentially caused by an interaction between NH 3 and the Cu cations located in eight ring sites of the bulk of the zeolite and is independent of the NH 3 -SCR of NOx occurring at Cu six ring sites within the zeolite.

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Synthesis of High-Silica LTA and UFI Zeolites and NH₃–SCR Performance of Their Copper-Exchanged Form

Cited by 125 publications

References 31 publications

Fully Copper‐Exchanged High‐Silica LTA Zeolites as Unrivaled Hydrothermally Stable NH₃‐SCR Catalysts

Fully Copper‐Exchanged High‐Silica LTA Zeolites as Unrivaled Hydrothermally Stable NH₃‐SCR Catalysts

Advances in the Synthesis of Ferrierite Zeolite

Operando Spectroscopic Studies of Cu–SSZ-13 for NH3–SCR deNOx Investigates the Role of NH3 in Observed Cu(II) Reduction at High NO Conversions

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Synthesis of High-Silica LTA and UFI Zeolites and NH3–SCR Performance of Their Copper-Exchanged Form

Cited by 125 publications

References 31 publications

Fully Copper‐Exchanged High‐Silica LTA Zeolites as Unrivaled Hydrothermally Stable NH3‐SCR Catalysts

Fully Copper‐Exchanged High‐Silica LTA Zeolites as Unrivaled Hydrothermally Stable NH3‐SCR Catalysts

Advances in the Synthesis of Ferrierite Zeolite

Operando Spectroscopic Studies of Cu–SSZ-13 for NH3–SCR deNOx Investigates the Role of NH3 in Observed Cu(II) Reduction at High NO Conversions

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Synthesis of High-Silica LTA and UFI Zeolites and NH₃–SCR Performance of Their Copper-Exchanged Form

Fully Copper‐Exchanged High‐Silica LTA Zeolites as Unrivaled Hydrothermally Stable NH₃‐SCR Catalysts

Fully Copper‐Exchanged High‐Silica LTA Zeolites as Unrivaled Hydrothermally Stable NH₃‐SCR Catalysts