Rational Design of a Novel Catalyst Cu‐SAPO‐42 for NH₃‐SCR Reaction

Abstract

vehicles have become stricter. At present, selective catalytic reduction of NO x with ammonia (NH 3-SCR) has been regarded as the most efficient technology to facilitate the NO x reduction in oxygen-rich exhaust released from diesel engines. [1-4] Metal-exchanged conventional aluminosilicate zeolites or silicoaluminophosphates (SAPO) molecular sieves (MSs) have been extensively investigated for catalyzing this reaction. Zeolites or SAPO MSs are a class of crystalline microporous materials with well-defined cavities or channels of molecular size. TO 4 tetrahedra (T = Al, Si, P, etc.) are considered as basic building units (BBUs). Until now, distinct 252 threedimensional (3D) zeolitic frameworks constructed by BBUs have been approved by IZA-structure committee. [5] They can be categorized into small pore (delimited by 8 T), medium pore (10 T), large pore (12 T), and extra-large pore (>12 T) MSs. Thereinto, small pore MSs, especially aluminosilicate SSZ-13 and SAPO-34 with the identical CHA framework, have been regarded as the efficient catalysts for the NH 3-SCR reaction due to their high NO x conversion and N 2 selectivity. [3] Although Cu-SSZ-13 catalyst has been commercialized, its thermal durability after the high-temperature (HT) hydrothermal aging, arising from the regeneration process of diesel particulate filter (DPF), can be further improved. Moreover, Cu-SAPO-34 catalyst has some disputes on the low-temperature (LT) hydrothermal stability. Therefore, it stimulates the interest of researchers to explore other novel zeolite frameworks with small pore openings. Recently, Hong et al. have reported a Cu exchanged LTA-type high-silica (3D 8 × 8 × 8-ring channel system) zeolite which has the better activity and durability than Cu-SSZ-13 after HT hydrothermal aging. [6,7] However, the expensive organic structure-directing agents (OSDAs) and the presence of the toxic fluoride used in its recipe might inhibit its further utilization as an NH 3-SCR catalyst. It is of interest to note that SAPO-42 with the LTA topology might be a potential catalyst for the NH 3-SCR reaction. The initial synthesis of SAPO-42 templated by TMA + and Na + was reported in 1984. [8,9] Strictly speaking, it is not an exact SAPO since only a few portions of phosphor are incorporated into the framework. After that, several works reported the synthesis of SAPO-42 by using complex OSDAs in the fluoride system or the ionothermal synthesis. [10-13] For example, Corma's Cu-exchanged LTA-type aluminosilicate catalyst has been considered as an efficient catalyst for the selective catalytic reduction of NO x with ammonia (NH 3-SCR). However, expensive organic structure-directing agents (OSDAs) and the corrosive fluoride medium are inevitably used to synthesize LTA-type molecular sieve (high-silica LTA-type aluminosilicate and its analogue LTAtype silicoaluminophosphate SAPO-42). Herein, a series of cheap and commercialized OSDAs, which are successfully applied for the targeted synthesis of SAPO-42 in the fluoride-free system, are identified by a nove...

Constrained Al sites in FER-type zeolites

“…For example, a 1D 12-ring aluminophosphate molecular sieve UiO-6 (OSI) and a 1D 8-ring aluminosilicate ERS-7 (ESV) were solved by simulated annealing algorithm [28,29]. Recently, it has been extended to investigate host-guest interactions in the crystalline porous materials [30,31]. After determining the initial positions of OSDAs, such parameters as atomic coordinates (framework atoms and guest species), unit cell dimensions, peak shape functions, background, etc.…”

Revealing the Specific Spatial Confinement in 8‐membered Ring Cage‐type Molecular Sieves via Solid‐state NMR and Theoretical Calculations

“…As mentioned above, methanol preferentially interacts with the molecular sieve by hydrogen‐bond instead of simple physical adsorption, [24,25] and methanol molecules probably associate with each other to form protonated dimer or cluster complex of methanol at high concentration, owing to its limited number of BASs [27] . The BAS of the employed SAPO‐42 has been proven to be located in site O1 by Rietveld Refinement in our previous work, by the usage of specific organic structure‐directing agent (OSDA) [30,31] . Thus, the single BAS and sole confined space of lta provide exclusive adsorption site for methanol, and the increasing trend of the SAPO‐42 is predominantly attributed to the interactions between adsorbate molecules, such as H‐bonding interactions.…”

“…[27] The BAS of the employed SAPO-42 has been proven to be located in site O1 by Rietveld Refinement in our previous work, by the usage of specific organic structure-directing agent (OSDA). [30,31] Thus, the single BAS and sole confined space of lta provide exclusive adsorption site for methanol, and the increasing trend of the SAPO-42 is predominantly attributed to the interactions between adsorbate molecules, such as H-bonding interactions.…”

Insights on the seed selection criteria of SAPO-34 synthesis: structural units and their chemical microenvironment

“…[13][14][15][16][17] As the analogs of zeolites, SAPO molecular sieves have equally important industrial applications. [18][19][20][21][22][23] In particular, SAPO-34, as an excellent methanol-to-olefins (MTO) catalyst, has received extensive attention, 24,25 and its catalytic performance has been optimized through the seed-assisted synthesis. 16,[26][27][28][29] However, it seems that only nanosized SAPO-34 seeds 30,31 or ball-milled SAPO-34 seeds with low crystallinity 15,26,28,[32][33][34] are feasible.…”