Direct synthesis design of Cu-SAPO-18, a very efficient catalyst for the SCR of NOx

Abstract

catalysts.-Complete framework Si isolation can be achieved for Cu-SAPO-18 materials.-Cu-SAPO-18 shows high catalytic activity and hydrothermal stability for SCR of NOx. KeywordsOne-pot synthesis, silicoaluminophosphate, SAPO-18, selective catalytic reduction (SCR), nitrogen oxides (NOx) 4 1.-IntroductionIn the last decades, small pore zeolites containing large cavities in their structure have become important industrial catalysts for the methanol-to-olefins (MTO) process, and for the field of gas separation.[1] In addition, these materials have recently broadened their applicability as efficient catalysts to control the emission of harmful gases, particularly nitrogen oxides (NOx) mainly produced during the high temperature combustion in diesel engines. [1,2] Indeed, the selective catalytic reduction (SCR) of NOx by ammonia or urea has been reported as the most widely applied emission control, [3] and copper-exchanged small pore CHA materials as one of the preferred catalysts (either as silicoaluminate, Cu-SSZ-13, [1,2,4] or as silicoaluminophosphate, Cu-SAPO-34). [2,5] Small pore Cu-CHA shows higher catalytic activities and hydrothermal stabilities for the SCR of NOx than other previously studied zeolites with larger pores (as Cu-Beta or Cu-ZSM-5, among others). [6] This is a very important point because the SCR of NOx reaction is performed in the presence of steam at high temperatures (above 400ºC) and, under these severe conditions, Cu-Beta or Cu-ZSM-5 zeolites suffer from permanent deactivation.[6]Specific stabilization issues by coordination of extra-framework Cu 2+ cations to three oxygen atoms of the double 6-rings (D6R) units present in the CHA structure have been described as the main reason of the improved catalytic activity and hydrothermal stability of the Cu-CHA catalysts.[7]Besides Cu-exchanged CHA, other Cu-exchanged small pore silicoaluminates containing D6R in their structure have been reported as efficient catalyst for the SCR of NOx, as Cu-SSZ-16 [8] and Cu-SSZ-39. [9] Particularly, Cu-SSZ-39, which presents the AEI structure, shows very high catalytic activity and hydrothermal stability for the SCR of NOx, even higher than commercial Cu-SSZ-13 catalyst. [9] Unfortunately, the range of preparation conditions of the silicoaluminate SSZ-39 is very limited, requiring very narrow Si/Al synthesis ratios (~30) and specific chemical sources, as for instance partially dealuminated USY and sodium silicate as Al and Si sources, respectively.[10] Moreover, the relatively low Si/Al ratios of the final SSZ-39 materials (~7-10) compared to the synthesis Si/Al ratios, 5 indicate that the solid yields are low (< 50%wt of initial oxides), [9,10] and this fact precludes possible industrial applications.The AEI structure has also been reported as silicoaluminophosphate form, SAPO-18, [11] which is mainly synthesized using N,N-diisopropylethylamine (DIPEA) as organic structure directing agent (OSDA). [11,12] SAPO-18 has been thoroughly used as catalyst for the MTO reaction, [13] but very few descriptions ca...

Zeolitic Materials for DeNOx Selective Catalytic Reduction

“…Our group reported that Cu‐SAPO‐44 exhibits excellent activity and N 2 selectivity over the wide temperature window from 200 to 550 °C . Because of the similar double six‐ring (D6R) structure in AEI and CHA zeolites, AEI‐type Cu‐SSZ‐39, Fe‐SSZ‐39, and Cu‐SAPO‐18 zeolites have been developed and exhibit excellent low‐temperature activity and high hydrothermal stability. Picone et al.…”

Understanding the structure directing action of copper–polyamine complexes in the direct synthesis of Cu-SAPO-34 and Cu-SAPO-18 catalysts for the selective catalytic reduction of NO with NH3

“…The work targeted the synthesis of Cu-SAPOs, because of their relevance to selective catalytic reduction, but investigation of one-pot synthesis using Ni 18 in this work from that of Corma and co-workers [12] is that whereas a template, N,N-dimethyl-3,5-dimethylpiperidinium, is used in that work to direct the synthesis of the SAPO-18, entraining Cu 2+ and/or Cu 2+ complex at the same time, in our synthesis it is the Cu-232 complex that directs crystallisation of the AEI structure.…”

“…In previous papers reporting the direct synthesis of Cu-SSZ-13, [7] Cu-SAPO-34 [9][10][11] and Cu-SAPO-18 [12] using Cu The main difference between the method of synthesis in this work from that of Corma and co-workers, [12] is that whereas a template, N,N-dimethyl-3,5-dimethylpiperidinium, is used in that work to direct the synthesis of the SAPO-18, entraining Cu 2+ and/or Cu 2+ complex at the same time, in our synthesis it is the Cu-232…”

“…[6][7][8][9][10][11][12] Calcination then releases the Cu 2+ cations to extra-framework sites distributed throughout the crystals and removes the need for a cation-exchange step. This process was first demonstrated for SAPO STA-7, [6] and subsequently for SSZ-13, [7] SAPO-34, [9][10][11] and very recently for SAPO-18 [12] giving active, selective and hydrothermally stable catalysts. The details of the mechanism by which the calcination of the complex-bearing precursor to SAPO STA-7 gives a porous, acidic framework with dispersed copper cations has been followed by ex situ UV-visible spectroscopy and by in situ microcrystal IR spectroscopy.…”

Efficient synthesis of the Cu-SSZ-39 catalyst for DeNOx applications

“…Recently, it has been described the direct synthesis of Cu-SSZ-13 [13] and other related Cu-containing silicoaluminophosphate materials, such as Cu-SAPO-34 [12d, [14]] and Cu-7 SAPO-18, [15] using the combination of an organometallic Cu-complex (Cu-TEPA) and a cooperative organic molecule as OSDA. Following a similar "one-pot" synthesis procedure combining Cu-TEPA and N,N-dimethyl-3,5-dimethylpiperidinium as cooperative OSDAs, a crystalline Cu-containing SSZ-39 material has been achieved (see supporting information for experimental details and the PXRD pattern of Cu-SSZ-39 in Figure 1).…”