Nanoscale intimacy in bifunctional catalysts for selective conversion of hydrocarbons

The ability to control nanoscale features precisely is increasingly being exploited to develop and improve monofunctional catalysts(1-4). Striking effects might also be expected in the case of bifunctional catalysts, which are important in the hydrocracking of fossil and renewable hydrocarbon sources to provide high-quality diesel fuel(5-7). Such bifunctional hydrocracking catalysts contain metal sites and acid sites, and for more than 50 years the so-called intimacy criterion(8) has dictated the maximum distance between the two types of site, beyond which catalytic activity decreases. A lack of synthesis and material-characterization methods with nanometre precision has long prevented in-depth exploration of the intimacy criterion, which has often been interpreted simply as 'the closer the better' for positioning metal and acid sites(8-11). Here we show for a bifunctional catalyst-comprising an intimate mixture of zeolite Y and alumina binder, and with platinum metal controllably deposited on either the zeolite or the binder-that closest proximity between metal and zeolite acid sites can be detrimental. Specifically, the selectivity when cracking large hydrocarbon feedstock molecules for high-quality diesel production is optimized with the catalyst that contains platinum on the binder, that is, with a nanoscale rather than closest intimacy of the metal and acid sites. Thus, cracking of the large and complex hydrocarbon molecules that are typically derived from alternative sources, such as gas-to-liquid technology, vegetable oil or algal oil(6,7), should benefit especially from bifunctional catalysts that avoid locating platinum on the zeolite (the traditionally assumed optimal location). More generally, we anticipate that the ability demonstrated here to spatially organize different active sites at the nanoscale will benefit the further development and optimization of the emerging generation of multifunctional catalysts(12-15)

Nanoscale intimacy in bifunctional catalysts for selective conversion of hydrocarbons

The ability to control nanoscale features precisely is increasingly being exploited to develop and improve monofunctional catalysts(1-4). Striking effects might also be expected in the case of bifunctional catalysts, which are important in the hydrocracking of fossil and renewable hydrocarbon sources to provide high-quality diesel fuel(5-7). Such bifunctional hydrocracking catalysts contain metal sites and acid sites, and for more than 50 years the so-called intimacy criterion(8) has dictated the maximum distance between the two types of site, beyond which catalytic activity decreases. A lack of synthesis and material-characterization methods with nanometre precision has long prevented in-depth exploration of the intimacy criterion, which has often been interpreted simply as 'the closer the better' for positioning metal and acid sites(8-11). Here we show for a bifunctional catalyst-comprising an intimate mixture of zeolite Y and alumina binder, and with platinum metal controllably deposited on either the zeolite or the binder-that closest proximity between metal and zeolite acid sites can be detrimental. Specifically, the selectivity when cracking large hydrocarbon feedstock molecules for high-quality diesel production is optimized with the catalyst that contains platinum on the binder, that is, with a nanoscale rather than closest intimacy of the metal and acid sites. Thus, cracking of the large and complex hydrocarbon molecules that are typically derived from alternative sources, such as gas-to-liquid technology, vegetable oil or algal oil(6,7), should benefit especially from bifunctional catalysts that avoid locating platinum on the zeolite (the traditionally assumed optimal location). More generally, we anticipate that the ability demonstrated here to spatially organize different active sites at the nanoscale will benefit the further development and optimization of the emerging generation of multifunctional catalysts(12-15)

Hydroisomerization of Emerging Renewable Hydrocarbons using Hierarchical Pt/H-ZSM-22 Catalyst

International audienc

Hydroisomerization and hydrocracking of linear and multibranched long model alkanes on hierarchical Pt/ZSM-22 zeolite

Hydroisomerization and hydrocracking using bifunctional zeolite catalysts with hydrogenation-dehydrogenation next to the Brønsted acid functionality are at the heart of key refinery processes converting heavy petroleum fractions to high grade lubricants and fuels. Hierarchical zeolites presenting a network of auxiliary mesoporosity in addition to their native microporosity are known to improve accessibility to their active sites. In this paper we assess the impact of hierarchization by demetallation of the well-established hydroisomerization catalyst Pt/ZSM-22 on the reaction pathways of the n-decane, n-nonadecane and pristane (2,6,10,14-tetramethylpentadecane) model molecules. Detailed analysis of reaction products and assessment of acid site accessibility in conventional and hierarchical ZSM-22 samples highlight the contributions of acid sites in pore mouths and micropores to the skeletal rearrangement and cracking reactions. © 2013 Elsevier B.V. All rights reserved.publisher: Elsevier articletitle: Hydroisomerization and hydrocracking of linear and multibranched long model alkanes on hierarchical Pt/ZSM-22 zeolite journaltitle: Catalysis Today articlelink: http://dx.doi.org/10.1016/j.cattod.2013.03.041 content_type: article copyright: Copyright © 2013 Published by Elsevier B.V.status: publishe

Hydroisomerization of Emerging Renewable Hydrocarbons using Hierarchical Pt/H-ZSM-22 Catalyst

International audienc

Hydroisomerization and hydrocracking of linear and multibranched long model alkanes on hierarchical Pt/ZSM-22 zeolite

International audienceHydroisomerization and hydrocracking using bifunctional zeolite catalysts with hydrogenationdehydrogenation next to the Bronsted acid functionality are at the heart of key refinery processes converting heavy petroleum fractions to high grade lubricants and fuels. Hierarchical zeolites presenting a network of auxiliary mesoporosity in addition to their native microporosity are known to improve accessibility to their active sites. In this paper we assess the impact of hierarchization by demetallation of the well-established hydroisomerization catalyst Pt/ZSM-22 on the reaction pathways of the n-decane, n-nonadecane and pristane (2,6,10,14-tetramethylpentadecane) model molecules. Detailed analysis of reaction products and assessment of acid site accessibility in conventional and hierarchical ZSM-22 samples highlight the contributions of acid sites in pore mouths and micropores to the skeletal rearrangement and cracking reactions. (C) 2013 Published by Elsevier B.V

Hydroisomerization and hydrocracking of linear and multibranched long model alkanes on hierarchical Pt/ZSM-22 zeolite

International audienceHydroisomerization and hydrocracking using bifunctional zeolite catalysts with hydrogenationdehydrogenation next to the Bronsted acid functionality are at the heart of key refinery processes converting heavy petroleum fractions to high grade lubricants and fuels. Hierarchical zeolites presenting a network of auxiliary mesoporosity in addition to their native microporosity are known to improve accessibility to their active sites. In this paper we assess the impact of hierarchization by demetallation of the well-established hydroisomerization catalyst Pt/ZSM-22 on the reaction pathways of the n-decane, n-nonadecane and pristane (2,6,10,14-tetramethylpentadecane) model molecules. Detailed analysis of reaction products and assessment of acid site accessibility in conventional and hierarchical ZSM-22 samples highlight the contributions of acid sites in pore mouths and micropores to the skeletal rearrangement and cracking reactions. (C) 2013 Published by Elsevier B.V

Aluminium atomic layer deposition applied to mesoporous zeolites for acid catalytic activity enhancement

Atomic Layer Deposition (ALD) of aluminium is a new method for enhancing acidity and acid catalytic activity in mesoporous zeolites and hierarchical materials

Prediction of Cu Zeolite NH₃-SCR Activity from Variable Temperature ¹H NMR Spectroscopy

Selective catalytic reduction (SCR) of NOx by ammonia is one of the dominant pollution abatement technologies for near-zero NOx emission diesel engines. A crucial step in the reduction of NOx to N2 with Cu zeolite NH3-SCR catalysts is the generation of a multi-electron donating active site, implying the permanent or transient dimerization of Cu ions. Cu atom mobility has been implicated by computational chemistry as a key factor in this process. This report demonstrates how variable temperature 1H NMR reveals the Cu induced generation of sharp 1H resonances associated with a low concentration of sites on the zeolite. The onset temperature of the appearance of these signals was found to strongly correlate with the NH3-SCR activity and was observed for a range of catalysts covering multiple frameworks (CHA, AEI, AFX, ERI, ERI-CHA, ERI-OFF, *BEA), with different Si/Al ratios and different Cu contents. The results point towards universal applicability of variable temperature NMR to predict the activity of a Cu-zeolite SCR catalyst. The unique relationship of a spectroscopic feature with catalytic behavior for zeolites with different structures and chemical compositions is exceptional in heterogeneous catalysis