NH3-SCR over Cu/SAPO-34 catalysts with various acid contents and low Cu loading

Yu, Tie; Wang, Jun; Shen, Meiqing; Li, Wei

doi:10.1039/c3cy00453h

Cited by 112 publications

(82 citation statements)

References 26 publications

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“…As has been observed for small-pore zeolites, this reaction over Cu/SAPO-34 produces very little NO 2 , with a maximum under 6% [38,39]. The trend with copper loading is similar to that seen with NH 3 oxidation: increasing up to 1.78 wt % Cu with little increase thereafter.…”

Section: Standard Scrsupporting

confidence: 59%

Impact of Copper Loading on NH3-Selective Catalytic Reduction, Oxidation Reactions and N2O Formation over Cu/SAPO-34

et al. 2017

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Abstract:We developed a procedure for aqueous ion exchange to obtain different Cu loadings of Cu/SAPO-34 (between 0 and 2.6 wt %). The catalysts were washcoated on monoliths and characterised with respect to their activity and selectivity under standard selective catalytic reduction (SCR), fast SCR, NH 3 oxidation and NO oxidation reactions. They were further characterised using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), H 2 -temperature programmed reduction (H 2 -TPR), ultraviolet (UV)-vis spectroscopy and NH 3 adsorption. As expected, activity of all reactions increased with copper loading, due to increased number of active sites. However, the N 2 O formation during standard and fast SCR yielded interesting mechanistic information. We observed that N 2 O formation at low temperature increased with copper loading for the standard SCR reaction, while it decreased for fast SCR. The low-temperature N 2 O formation during fast SCR thus occurs predominantly over Brønsted sites. Species responsible for N 2 O formation during standard SCR, on the other hand, are formed on the copper sites. We further found that the fast SCR reaction occurs to a significant extent even over the H/SAPO-34 form. The Brønsted sites in SAPO-34 are thus active for the fast SCR reaction.

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Section: Standard Scrsupporting

confidence: 59%

Impact of Copper Loading on NH3-Selective Catalytic Reduction, Oxidation Reactions and N2O Formation over Cu/SAPO-34

et al. 2017

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“…As it can be seen in Figure S1, the SAPO-18 samples show the presence of different ammonia desorption peaks at different temperatures. The first peak centered at 180ºC has been assigned to weak acid sites corresponding to P-OH hydroxyl groups, [27] and the peaks centered at 375ºC and 425 would indicate the presence of medium and strong acid sites, respectively, which would correspond to the acidic protons associated with the presence of isolated silicon species in the zeolitic framework. [27] The quantification of the desorbed ammonia for the Si-rich SAPO-18 materials [Si/TO 2 ~0.08, see Table 3], reveals that the SAPO-18_1 sample shows higher concentration of weak acid sites (0.16 mmol NH 3 /g) and less concentration of medium-strong acid sites (0.35 + 0 mmol NH 3 /g) than the SAPO-18_3 sample (0.11, and 0.49 + 0.22 mmol NH 3 /g, respectively, see Table 3).…”

Section: 1-zeolite Synthesis and Characterizationmentioning

confidence: 99%

Improving the catalytic performance of SAPO-18 for the methanol-to-olefins (MTO) reaction by controlling the Si distribution and crystal size

Martínez-Franco

Martínez‐Triguero

et al. 2016

Catal. Sci. Technol.

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The physico-chemical properties of the small pore SAPO-18 zeotype have been controlled by properly selecting the organic molecules acting as organic structure directing agents (OSDAs). The two organic molecules selected to attempt the synthesis of the SAPO-18 materials were N,N-diisopropylethylamine (DIPEA) and N,N-dimethyl-3,5-dimethylpiperidinium (DMDMP). On one hand, DIPEA allows achieving small crystal sizes (0.1-0.3 µm) with limited silicon distributions when the silicon content in the synthesis gel is high (Si/TO 2 ~ 0.8). On the other hand, the use of DMDMP directs the formation of larger crystallites (0.9-1.0 µm) with excellent silicon distributions, even when the silicon content in the synthesis media is high (Si/TO 2 ~ 0.8). It is worth noting that this is the first description of the use of DMDMP as OSDA for the synthesis of the SAPO-18 material, revealing not only the excellent directing role of this OSDA to stabilize the large cavities present in the SAPO-18 structure, but also to selectively place the silicon atoms in isolated framework positions. The synthesized SAPO-18 materials have been characterized by different techniques, such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), N 2 adsorption, solid NMR, or ammonia temperature programmed desorption (NH 3 -TPD). Finally, their catalytic activity has been evaluated for the Methanol-to-Olefin (MTO) process at different reaction temperatures (350 and 400ºC), revealing that the SAPO-18 catalysts with optimized silicon distributions and crystal sizes show excellent catalytic properties for the MTO reaction. These optimized SAPO-18 materials present improved catalyst lifetimes compared to standard SAPO-34 and SSZ-39 catalysts, even when tested at low reaction temperatures (i.e. 350ºC). 3 1.-IntroductionThe Methanol-to-Olefins (MTO) process has received a significant attention in the last years since it has been considered as an alternative route for the production of light olefins, such as ethylene and propylene, which are currently mainly achieved from fluid catalytic cracking or steam cracking of hydrocarbons. [1,2] Small pore silicoaluminophosphate (SAPO) materials containing large cavities in their structures, have been described as the most efficient catalysts for the MTO reaction. [2,3] Indeed, SAPO-34 material, which is the silicoaluminophosphate form of the crystalline structure of CHA, [4] is being applied as commercial catalyst for this process. [3,5] It is claimed that the unique crystalline structure of CHA, combining the presence of large cavities (~ 6.7x10.9 Å) and small pores (~ 3.8 Å), allows the formation of the required bulky aromatic intermediate states, known as "hydrocarbon pool", and permits the preferential diffusion of the desired light olefins, respectively. [6,7,8,9,10] In addition to the SAPO-34 catalyst, other small pore SAPO materials presenting large cavities in their structure have also been studied as catalysts for the MTO process. [11,12] From the different SAPO materials, SAPO-18 has sho...

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“…Korhonen et al 10 proposed that isolated Cu 2+ was the active site of NH 3 -SCR for the first time in 2011 with operando UV-Vis spectroscopic results, and it is now widely accepted by researchers that this Cu 2+ locates slightly above the six-membered ring of CHA-type zeolites in a dehydrated sample with low Cu loading. [11][12][13][14][15] The nature of Cu species during the reaction, however, still has not been clari-fied. Some researchers 16,17 argued that a mixture of Cu(I)-Cu(II) oxidation states will exist during standard SCR process, but it is not generally accepted yet.…”

Section: Introductionmentioning

confidence: 99%

Understanding Catalytic Reactions over Zeolites: A Density Functional Theory Study of Selective Catalytic Reduction of NO_x by NH₃ over Cu-SAPO-34

Wang²,

et al. 2016

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Metal exchanged CHA-type (SAPO-34 and SSZ-13) zeolites are currently promising catalysts for selective catalytic reduction (SCR) of NO x by NH 3 . However, the understanding of above process at the molecular level is still limited, which hinders the identification of its mechanism and the design of more efficient zeolite catalysts. In this work, modelling over Cu-SAPO-34, a comprehensive periodic density functional theory (DFT) study of NH 3 -SCR is performed with the consideration of van der Waals (vdW) interactions. A novel N-N coupling mechanism (energy barrier 0.33 eV) with verified transition state is proposed to account for the activation of NO. The redox cycle of Cu 2+ and Cu + , which is crucial for the SCR process because O 2 can only be activated on the Cu + site, is identified with detailed analysis. Besides, the decomposition of NH 2 NO is calculated to be readily occur on the Brønsted acid site by a hydrogen push-pull mechanism, confirming the collective efforts of Brønsted acid and Lewis acid (Cu 2+ ) sites. More importantly, the unique electronic and structural properties of zeolites are proved to play a essential role in all above reaction features in this study, which may have a general implication on the understanding of zeolite catalysis.

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NH3-SCR over Cu/SAPO-34 catalysts with various acid contents and low Cu loading

Cited by 112 publications

References 26 publications

Impact of Copper Loading on NH3-Selective Catalytic Reduction, Oxidation Reactions and N2O Formation over Cu/SAPO-34

Impact of Copper Loading on NH3-Selective Catalytic Reduction, Oxidation Reactions and N2O Formation over Cu/SAPO-34

Improving the catalytic performance of SAPO-18 for the methanol-to-olefins (MTO) reaction by controlling the Si distribution and crystal size

Understanding Catalytic Reactions over Zeolites: A Density Functional Theory Study of Selective Catalytic Reduction of NO_x by NH₃ over Cu-SAPO-34

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NH3-SCR over Cu/SAPO-34 catalysts with various acid contents and low Cu loading

Cited by 112 publications

References 26 publications

Impact of Copper Loading on NH3-Selective Catalytic Reduction, Oxidation Reactions and N2O Formation over Cu/SAPO-34

Impact of Copper Loading on NH3-Selective Catalytic Reduction, Oxidation Reactions and N2O Formation over Cu/SAPO-34

Improving the catalytic performance of SAPO-18 for the methanol-to-olefins (MTO) reaction by controlling the Si distribution and crystal size

Understanding Catalytic Reactions over Zeolites: A Density Functional Theory Study of Selective Catalytic Reduction of NOx by NH3 over Cu-SAPO-34

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Understanding Catalytic Reactions over Zeolites: A Density Functional Theory Study of Selective Catalytic Reduction of NO_x by NH₃ over Cu-SAPO-34