Desilication of ZSM-5 and ZSM-12 zeolites: Impact on textural, acidic and catalytic properties

Influence of lattice stability on hydrothermal deactivation of Cu-ZSM-5 and Cu-IM-5 zeolites for selective catalytic reduction of NOx by NH3

“…The changes in catalyst structure 29 that occur during ageing are i) partial dealumination of the zeolite, ii) reversible migration of copper 30 species, and iii) irreversible formation of catalytically inactive and stable Cu-Al clusters, which 31 have some resemblance to CuAl 2 O 4 , but without the symmetry of Cu in this spinel structure. As the 32 Cu-Al clusters only form once Al is detached from the framework, the stability of Al in the zeolite 33 framework is proposed to dictate the overall hydrothermal deactivation behavior of Cu-ZSM-5 and 37 38 Selective catalytic reduction (SCR) of nitrogen oxides (NO x ) with NH 3 is an important technology 39 for reducing environmentally harmful NO x in the exhaust gases from vehicles, ships, and power 40 plants to the emission levels required by legislation. As legislation is becoming more stringent 41 further development of SCR-technologies and a better understanding of the catalytic materials are dispersed [11], and in this case the stability of the zeolite framework should be less important When 70 copper is loaded into zeolite structures containing small pores, such as the CHA or AEI topologies, 71 a more stable activity is observed, possibly because of the limited migration of detached aluminum 72 moeities inside the pores [12,13].…”

Geração de mesoporos em zeólitas ZSM-5 e seus efeitos na conversão do etanol em olefinas

“…Para as três amostras estudadas, os espectros de MAS/RMN do 29 Si apresentaram um pico intenso em aproximadamente -115 ppm, correspondente aos átomos de silício ligados a quatro outros átomos de silício (4Si-0Al) através do átomo de oxigênio. 13 No caso das amostras HZSM-5 e BZSM-5, foi observada a presença de um segundo pico a cerca de -109 ppm, atribuído aos átomos de silício ligados a três : calculado pelo método BJH outros átomos de silício e a um átomo de alumínio (3Si-1Al), também através de átomo de oxigênio comum. 13 Os espectros de MAS/RMN do 27 Al apresentaram dois picos principais.…”

“…13 No caso das amostras HZSM-5 e BZSM-5, foi observada a presença de um segundo pico a cerca de -109 ppm, atribuído aos átomos de silício ligados a três : calculado pelo método BJH outros átomos de silício e a um átomo de alumínio (3Si-1Al), também através de átomo de oxigênio comum. 13 Os espectros de MAS/RMN do 27 Al apresentaram dois picos principais. Um correspondente ao alumínio em coordenação tetraé-drica, associado ao alumínio da rede cristalina da zeólita, a cerca de 55 ppm, e outro, com deslocamento em torno de 0,5 ppm, associado ao alumínio em coordenação octaédrica e correspondente às espécies extrarreticulares (ALER).…”

Synthesis of nano-SSZ-13 and its application in the reaction of methanol to olefins

“…4 Following this, much effort has been devoted, especially with ZSM-5, on the direct synthesis of hierarchical zeolites, by means of: a)dual templating with hard and soft secondary SDAs, [5][6][7][8] b)single multifunctional templates, 9, 10 c)varying synthesis conditions to decrease the size of the crystals 11,12 or by postsynthesis leaching treatments. 4,[13][14][15][16] In the case of SAPO-34, its performance has been improved by developing mesopores [17][18][19][20][21][22] and by synthesizing crystals of smaller size. [23][24][25][26][27][28][29][30][31] The use of dual templates, which implies small organic struture directing agent for the formation of micropores and large organic molecular surfactants for developing mesopores as a strategy to prepare meso-MFI, has been proposed 32,33 .…”