Improvement of Lifetime Using Transition Metal‐Incorporated SAPO‐34 Catalysts in Conversion of Dimethyl Ether to Light Olefins

Abstract

Transition metal (Mn, Fe, or Ni) incorporated nanocatalysts were synthesized using a hydrothermal method to improve the catalytic lifetime in the conversion of dimethyl ether to light olefins (DTO). The structures of the synthesized catalysts were characterized using several methods including XRD, SEM, BET, 29 Si-MAS NMR, and NH 3 -TPD techniques. Although the structure of the MeAPSO-34 catalysts was similar to that of the SAPO-34 catalyst, the amount of weak acid sites in all MeAPSO-34 catalysts was markedly increased and accompanied by differences in crystallinity and structural arrangement. The amount of weak acid sites decreased in the following order: NiAPSO-34 > FeAPSO-34 > MnAPSO-34 > SAPO-34 catalyst. The MeAPSO-34 catalysts, when used in the DTO reaction, maintained DME conversion above 90% for a longer time than the SAPO-34 catalyst, while also maintaining the total selectivity above 95% for light olefins. In addition, the NiAPSO-34 catalyst showed the longest catalytic lifetime; the lifetime was extended approximately 2-fold relative to the SAPO-34 catalyst. Therefore, the increase in the catalytic lifetime is related to the amount of weak acidic sites, and these sites are increased in number by incorporating transition metals into the SAPO-34 catalyst.

Synthesis of Small-Sized SAPO-34 Crystals with Varying Template Combinations for the Conversion of Methanol to Olefins

“…Compared to a single template, the use of a composite tri-templating agent resulted in an increase in the relative contents of Si(3Al), Si(2Al), Si(1Al), and Si(0Al) structures. Combined with the distribution of the acid properties on the molecular sieves of different template agents synthesized in Table 4 as the size of the silica islands increased, the acid strength of the molecular sieves increased Figure 7 shows the Si environment in the SAPO-34 framework studied by 29 Si MAS NMR. From the 29 Si MAS NMR spectrum, it can be seen that S-1 and S-3 all showed strong resonance peaks at δ = −90.6 [24], corresponding to the Si(4Al) structure.…”

“…The total acid amount of the molecular sieve also varied with the type of templating agent, and the total acid content of S-3 was the largest, followed by S-2, and S-1 was the smallest and the use of a composite templating agent was beneficial to increase the amount of acid in the molecular sieve. Figure 7 shows the Si environment in the SAPO-34 framework studied by 29 Si MAS NMR. From the 29 Si MAS NMR spectrum, it can be seen that S-1 and S-3 all showed strong resonance peaks at δ = −90.6 [24], corresponding to the Si(4Al) structure.…”

“…Figure 7 shows the Si environment in the SAPO-34 framework studied by 29 Si MAS NMR. From the 29 Si MAS NMR spectrum, it can be seen that S-1 and S-3 all showed strong resonance peaks at δ = −90.6 [24], corresponding to the Si(4Al) structure. This is due to the substitution of P atoms by Si atoms alone (SM2) [25].…”

“…The Mb of sample S-3 was 0, indicating that the templating agent in the sample cage of the molecular sieve was used to balance the skeleton charge. The proportions of the different template agents used to balance the charge of the framework followed the order S3 > S1, using the SM2 or SM3 substitution mechanism [26,28,29]. The negative ion of the skeleton was generated at the same time as the formation of the silicon island structure [28,30], so the more templating agents used to balance the skeleton charge and the greater the relative content of the Si structure distribution in the silicon island structure, the stronger the acidity exhibited by the molecular sieve was, which is consistent with the results presented in Tables 4 and 5.…”

“…In this work, SAPO-34 catalysts were synthesized using Mor, TEAOH, and TEA as templates, and the silicon to aluminum ratio was further tailored to improve the catalysts' performance. The synthesized catalysts were studied with XRD, SEM, N 2 adsorption-desorption, XRF, TG, NH 3 -TPD, FT-IR, and 29 Si MAS NMR characterization tests, and their catalytic performances were evaluated by taking MTO as the model reaction.…”