Rational direct synthesis methodology of very active and hydrothermally stable Cu-SAPO-34 molecular sieves for the SCR of NOx

Abstract

A one-pot direct synthesis of Cu-SAPO-34 has been achieved that allows more than 90% yield in the material synthesis. By this method it is easy to control the Cu-loading in the Cu-SAPO-34. It is presented that a maximum in hydrothermal stability with very high activity for NOx SCR with NH 3 is obtained for an optimum Cu loading. KeywordsOne-pot synthesis, silicoaluminophosphate, SAPO-34, selective catalytic reduction (SCR), nitrogen oxides (NOx) Highlights-Rational direct synthesis of Cu-SAPO-34 by using the co-directing templates.-Easy control of Cu-loading in Cu-SAPO-34 materials, and very high solid yields.-High activity and stability for SCR of NOx. In fact, the SCR of NOx experiment described by Xiao was performed on the sample with Si/Al ratio of 4.1 under mild conditions (low space velocity), and the stability of the synthesized samples under hydrothermal treatments was not studied. In addition to SSZ-13, the chabazite molecular sieve can be synthesized as silicoaluminophosphate form, . Cu-exchanged SAPO-34 has also been shown as a very stable and active material for SCR of NOx [14]. In the last years, some groups have attempted the direct preparation of Cu-SAPO-34 in order to achieve an inexpensive and more efficient synthetic route for this metal-substituted material [15].In those cases morfoline and copper oxide were used as organic structure directing with the tetraethylenepentamine (TEPA, 99%wt, Aldrich). This mixture was stirred for 2 hours until complete dissolution. Secondly, distilled water and phosphoric acid (85% wt, Aldrich) were added and stirred during 5 minutes. Third, alumina (75%wt, Condea) 7 and silica (Ludox AS40 40%wt, Aldrich) sources were introduced in the gel mixture.Finally, diethylamine (DEA, 99%wt, Aldrich) and SAPO-34 seeds (5%wt of expected final yield), if required, were added in the gel, and the mixture was stirred during 30 minutes. The resulting gel was transferred to an autoclave with a Teflon liner, and heated at 150ºC under static conditions during the required time (see experimental conditions for each sample in Table 1, Table 3, or Table 4). Crystalline products were filtered and washed with abundant water, and dried at 100ºC overnight. The samples were calcined at 550ºC in air to properly remove the occluded organic species. washed with distilled water, and dried at 100ºC overnight. The sample was calcined at 550ºC in air to remove the occluded organic species.In order to perform the Cu ion exchange on this SAPO-34 material, the calcined sample was first washed with NaNO 3 (0.04M), and afterwards, the sample was exchanged at room temperature with a Cu(CH 3 CO 2 ) 2 solution (solid/liquid ratio of 10g/L). Finally, the sample was filtered and washed with distilled water, and calcined at 550ºC for 4 h. 2.2.-CharacterizationX-ray diffraction (XRD) measurements were performed on a multisample Philips X'Pert diffractometer equipped with a graphite monochromator, operating at 40 kV and 45 mA, and usig Cu K α radiation (λ = 0,1542 nm).The chemical analyses were car...

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

“…[16,18] These results points out the relevance that the new Cu-containing SAPO-18 catalysts may have in the current De-NOx scenario if they show high hydrothermal stability after being treated under severe ageing conditions.…”

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).…”

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

“…We and others [9][10][11] have shown that the copper complexes of the linear polyamines triethylenetetramine and tetraethylenepentamine are suitable SDAs for SAPO-34, and that calcination gives active SCR catalysts. Linear polyamines are relatively affordable (compared to the azamacrocycle used in the synthesis of Cu-SAPO STA-7) so we set out to investigate the action of a range of copper complexes of the linear polyamines in the direct synthesis of Cu 2+ -containing SAPOs, and to understand the mechanism by which they direct crystallisation.…”

“…[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.…”