Shape-selective catalysis in zeolites

The isopropylation of naphthalene with propene over H-mordenite: The catalysis at the internal and external acid sites

“…Some zeolites are expected to offer unique shape-selective catalysis through the interaction of reactants, intermediates, and products with their pores and channels [1][2][3][4][5][6][7][8]. The shape-selective catalysis occurs through molecular recognition of organic molecules in their pores and channels of zeolites which can exclude the bulky reactants, intermediates, and/or products by the steric interaction with them, resulting in the formation of the less bulky products [2,[6][7][8].…”

“…The shape-selective catalysis occurs through molecular recognition of organic molecules in their pores and channels of zeolites which can exclude the bulky reactants, intermediates, and/or products by the steric interaction with them, resulting in the formation of the less bulky products [2,[6][7][8]. They are classified as "reactant selectivity", "product selectivity", and "restricted transition state selectivity" mechanisms [2,[4][5][6][7][8].…”

Produção de etilenoglicóis e derivados por reações catalíticas do óxido de eteno

“…A catálise com seletividade de forma é uma característica de peneiras moleculares microporosas (e. g. zeólitas) bastante utilizada em processos industriais, desde a sua descoberta como catalisadores 30 . Esta seletividade, que depende principalmente da estrutura da peneira, pode ser dividida em seletividade de forma a reagentes, produtos e a estados de transição [31][32][33] . As duas primeiras estão relacionadas com a maior ou menor difusão dos reagentes através dos canais microporosos da peneira e a última, a efeitos estéricos, devido ao espaço limitado para que a reação ocorra (Figura 4).…”

Supercritical catalysts of light hydrocarbon conversion. DOE PETC eighth quartery report, July 1, 1995--September 30, 1995

“…Catalysts such as zeolites with pore diameters about equal to molecular dimensions can exert strong steric influences in catalysis; the phenomena are referred to as shape-selective catalysis [34]. Narrow pores can exert strong repulsive forces on reactant molecules that just fit in them, and in the limiting case molecules that are too large to fit are excluded from any catalytic sites in the interior catalyst volume.…”

“…Product shape selectivity occurs when some products formed in the pores are too large to migrate readily through the apertures and out of the pores; thus their rate of entry into the product stream is hindered relative to that of other products. These are transport effects, and they are not discussed further Restricted transition state shape selectivity [34, is not a transport effect; it directly affects the reaction mechanism. It occurs when a transition state is large enough that it is subject to steric repulsion because of contact with the catalyst pore walls, which can retard the conversion of one reactant relative to that of another that forms a smaller transition state.…”