Absolute dissociation cross sections for D2 dissociation on Pt steps

Reaction mechanisms following gas-surface collisions may differ depending on the site of impact. On stepped Pt surfaces at least three dissociation mechanisms have been suggested to occur in parallel. Using supersonic molecular beams and a curved Pt single crystal, we unravel these site-dependent contributions and quantify absolute reaction cross sections using these mechanisms' different dependencies on kinetic energy in the range of 0.7 to 13.4 kJ/mol. A sum of three dissociation mechanism probabilities fits our data well and allows us to extract absolute cross sections for indirect and direct non-activated dissociation at steps. We find good agreement with theoretical predictions.Catalysis and Surface Chemistr

An inexpensive 3D printed periscope-type smartphone-based spectrophotometer for emission, absorption, and fluorescence spectrometry

We present the design of a periscope-type VIS spectrometer foreducational purposes that combines strong features from various earlier designs andadds new ones. Three 3D-printed pieces that hold a small thin mirror sheet, a 1/8thwedge of a DVD, and two razor blades are easily assembled and facilitate insight into itsconstruction. A new feature is the permanent attachment of theflexible back cover ofany smartphone, allowing for repeated removal and insertion of the smartphone withprecision alignment for recording spectra. An optional fourth 3D-printed piece actingas a container for a PMMA UV semimicrocuvette, a white LED and a UV LED, and a 9V battery attaches to the front. Beyond commonly applied absorption spectroscopywith similar devices, our design also allows forfluorescence spectroscopy. We reportresults of straightforward experiments illustrating the various uses of this less than $40MiniSpectroscope.Catalysis and Surface Chemistr

Chiral surface characterisation and reactivity toward H-D exchange of a curved platinum crystal

Understanding heterogeneous catalysis at the atomic level requires detailed knowledge of the reactivity of different surface sites toward specific bond breaking and bond making events. We illustrate a new method in such investigations. We use a macroscopically curved Pt single crystal containing a large variation in density of highly kinked steps of two different chiralities. Scanning tunneling microscopy maps the entire range of surface structures present on the 31 degrees section surrounding the Pt(111) apex. Whereas most of the surface shows the expected characteristic arrays of parallel steps, hexagonally-shaped, single-atom deep pits remain after cleaning procedures near the apex. Their orientation is indicative of the different chiralities present on the two sides of the crystal's apex. These unintended defects locally raise the surface defect concentration, but are of little consequence to subsequent reactivity measurements for D-2 dissociation and H-D exchange as probed by supersonic molecular beam techniques. We quantify absolute elementary dissociation and relative isotopic exchange rates across the surface with high spatial resolution. At low incident energies, elementary dissociation of the homonuclear isotoplogues is dominated by the kinked steps. H-D exchange kinetics depend also mostly linearly on step density. The changing ratio of D(2)dissociation to H-D formation, however, suggests that anisotropic diffusion of H(D) atoms is of influence to the measured HD production rate.Catalysis and Surface Chemistr

How to assess students' structure-property reasoning?

This paper describes the design of an instrument to property reasoning (SPR). Design criteria for the instrument required that it should be based on a comprehensive model for structure-property reasoning, assess both reproductive and productive use of structure-property reasoning, be cost-effective, and be easy for teachers to adapt to their situation. An unframed and framed sorting task and an unframed and framed mapping task were included in the instrument. It was used to determine the proficiency in structure-property reasoning of two populations: 60 Dutch secondary school students on the preuniversity track and 108 Dutch first-year university chemistry students. Results were analyzed using established statistical techniques, and they confirmed that the SPR-instrument clearly discriminates between preuniversity and first-year chemistry students. The paper concludes by outlining the possibilities offered by the instrument and suggestions for further research.Teaching and Teacher Learning (ICLON

Adsorption dynamics of O2 on Cu(111): a supersonic molecular beam study

We have studied the adsorption of O-2 on Cu(111) using supersonic molecular beam techniques. For incident energies ranging between 100 and 400 meV, we have determined the sticking probability as a function of angle of incidence, surface temperature, and coverage. Initial sticking probabilities range from near 0 to 0.85 with an onset near 100 meV, making Cu(111) considerably less reactive than Cu(110) and Cu(100). Normal energy scaling applies and reactivity increases appreciably over the entire range of surface temperatures from 90 to 670 K. A strictly linearly decreasing coverage dependence on sticking precludes adsorption and dissociation via an extrinsic or long-lived mobile precursor state. We cannot exclude that sticking also occurs molecularly at the lowest surface temperatures. However, all tell tales from our experiments suggest that sticking is predominantly direct and dissociative. Comparison to earlier data shows implications for the relative reactivity of Cu(111) vs. Cu/Ru(0001) overlayers.Catalysis and Surface Chemistr

Subsurface Oxygen on Pt(111) and Its Reactivity for CO Oxidation

Catalysis and Surface Chemistr

Comparative study of C-H stretch and bend vibrations in methane activation on Ni(100) and Ni(111)

Catalysis and Surface Chemistr

Heterogeneous Catalytic Oxidation of Simple Alcohols by Transition Metals

Catalysis and Surface Chemistr

Two design principles for the design of demonstrations to enhance structure–property reasoning

Structure–property reasoning (SPR) is one of the most important aims of chemistry education but is seldom explicitly taught, and students find structure–property reasoning difficult. This study assessed two design principles for the development of structure–property reasoning in the context of demonstrations: (1) use of a POE task (predict–observe–explain) and (2) use of the domain-specific particle perspective, both to increase student engagement and to scaffold micro-level modeling. The aim of the demonstration series was to teach structure–property reasoning more explicitly to pre-university students (aged 15–16). Demonstrations pertained to the properties of metals, salts and molecular compounds. The SPR instrument was used as a pretest and posttest in order to gain insight into the effects on structure–property reasoning. In addition, one student (Sally) was followed closely to see how her structure–property reasoning evolved throughout the demonstrations. Results show that after the demonstrations students were more aware of the structure models at the micro-level. The students also knew and understood more chemical concepts needed for structure–property reasoning. Sally’s qualitative data additionally showed how she made interesting progress in modeling micro-level chemical structures. As we used conventional demonstrations as a starting point for design, this could well serve as a practical tool for teachers to redesign their existing demonstrations.Teaching and Teacher Learning (ICLON