Diffusion of long n-alkanes in silicalite. A comparison between neutron scattering experiments and hierarchical simulation results

Jobic, H; Theodorou, DN

dc.contributor.author	Jobic, H	en
dc.contributor.author	Theodorou, DN	en
dc.date.accessioned	2014-03-01T01:24:00Z
dc.date.available	2014-03-01T01:24:00Z
dc.date.issued	2006	en
dc.identifier.issn	1520-6106	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/17160
dc.subject	Neutron Scattering	en
dc.subject.classification	Chemistry, Physical	en
dc.subject.other	Computer simulation	en
dc.subject.other	Diffusion	en
dc.subject.other	Molecular dynamics	en
dc.subject.other	Neutron scattering	en
dc.subject.other	Nuclear magnetic resonance	en
dc.subject.other	Silica	en
dc.subject.other	Brownian dynamics	en
dc.subject.other	Hierarchical simulation	en
dc.subject.other	Silicalites	en
dc.subject.other	Paraffins	en
dc.title	Diffusion of long n-alkanes in silicalite. A comparison between neutron scattering experiments and hierarchical simulation results	en
heal.type	journalArticle	en
heal.identifier.primary	10.1021/jp056924w	en
heal.identifier.secondary	http://dx.doi.org/10.1021/jp056924w	en
heal.language	English	en
heal.publicationDate	2006	en
heal.abstract	New quasi-elastic neutron scattering (QENS) data are presented for the self-diffusion of normal alkanes up to hexadecane in the zeolite silicalite at low occupancy. Measured diffusivities at 300 K are higher than in Na-ZSM-5 and agree with the predictions of molecular dynamics and a hierarchical transition-state theory/ Brownian dynamics conducted on the same systems. Activation energies for diffusion are around 5 kJ/mol for C1-C 6 but rise with carbon number for C8-C16 to approximately 15 kJ/mol for C16. An explanation is suggested by the hierarchical simulation, which finds that C1-C6 tend to reside entirely within the interiors of single channel segments and diffuse through jumps across energetically less favorable channel intersections, while longer molecules straddle channel intersections and must undergo conformational rearrangements in order to diffuse. The agreement between QENS and simulations reflects that the two methods probe motion over the same small (nm) length scales. Self-diffusivities measured by pulsed field gradient nuclear magnetic resonance (PFG-NMR) in the same systems are appreciably lower. This is because PFG-NMR probes motion over significantly longer (μm) length scales and is therefore more sensitive to defects in the silicalite crystals. © 2006 American Chemical Society.	en
heal.publisher	AMER CHEMICAL SOC	en
heal.journalName	Journal of Physical Chemistry B	en
dc.identifier.doi	10.1021/jp056924w	en
dc.identifier.isi	ISI:000235284300003	en
dc.identifier.volume	110	en
dc.identifier.issue	5	en
dc.identifier.spage	1964	en
dc.identifier.epage	1967	en