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1.
Artigo em Inglês | MEDLINE | ID: mdl-32749736

RESUMO

We determine absolute reactivities for dissociation at low coordinated Pt sites. Two curved Pt(111) single-crystal surfaces allow us to probe either straight or highly kinked step edges with molecules impinging at a low impact energy. A model extracts the average reactivity of inner and outer kink atoms, which is compared to the reactivity of straight A- and B-type steps. Local surface coordination numbers do not adequately capture reactivity trends for H2 dissociation. We utilize the increase of reactivity with step density to determine the area over which a step causes increased dissociation. This step-type specific reactive area extends beyond the step edge onto the (111) terrace. It defines the reaction cross-section for H2 dissociation at the step, bypassing assumptions about contributions of individual types of surface atoms. Our results stress the non-local nature of H2 interaction with a surface and provide insight into reactivity differences for nearly identical step sites.

2.
J Chem Educ ; 94(9): 1209-1216, 2017 Sep 12.
Artigo em Inglês | MEDLINE | ID: mdl-28919643

RESUMO

As it connects to a large set of important fundamental ideas in chemistry and analytical techniques discussed in high school chemistry curricula, we review the exploding flask demonstration. In this demonstration, methanol vapor is catalytically oxidized by a Pt wire catalyst in an open container. The exothermicity of reactions occurring at the catalytic surface heats the metal to the extent that it glows. When restricting reactant and product gas flow, conditions may favor repetitive occurrence of a small explosion. We show how mass spectrometry and infrared spectroscopy allow for unravelling the chemical background of this demonstration and discuss various ideas on how to use it in a classroom setting to engage students' critical thinking about chemical research. Along the way, we show that two commonly published ideas about the chemical background of this demonstration are incorrect, and we suggest simple tests that may be performed in a high school setting either as an addition to the demonstration or as a student research project.

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