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Multi-component heterogeneous catalysts are among the top candidates for converting greenhouse gases into valuable compounds. Combinations of Cu, Zn, and ZrO2(CZZ) have emerged as promisingly efficient catalysts for CO2hydrogenation to methanol. To explore the catalytic mechanism, density functional theory (DFT) calculations and the energetic span model (ESM) were used to study CO2conversion routes to methanol on CuZn–ZrO2interfaces with a varying Zn content. Our results demonstrate that the presence of Zn sites at the interface improves CO2binding. However, the adsorption and activation energies are insensitive to Zn concentration. The calculations also show that the hydrogenation of adsorbate oxygen atoms at the interface is kinetically more favourable and requires hydrogen spillover from the metal to the zirconia. This leads to barriers that are lower than those reported on interface or metal-only sites in previous literature. While DFT calculations alone are unable to identify which one of the competing pathways is more favourable, the ESM model predicts that the carboxyl pathway has a higher turnover frequency than the formate route. Our findings also show the importance of considering effects such as hydrogen spillover which take place at a metal-oxide interface when modelling complex catalytic environments.

Solid parahydrogen (p-H2) is known to support long-lived coherences, of the order of 100 ps, which enables high-resolution spectroscopy in the time domain. Rotational Raman-type excitations to sublevels of J = 2 are delocalized due to electric-quadrupole-quadrupole coupling in p-H2 crystals, and the resulting states can be characterized as rotons. Wave packets of rotons exhibit molecular alignment with respect to laboratory coordinates. Here the concept of field-free molecular alignment, induced by strong ultrashort laser pulses, is extended into a molecular solid case. We derive a solid-state analog for the gas-phase alignment measure and illustrate the time-dependent alignment degree in p-H2 crystals by numerical simulations. To underscore the Raman gain effect of the solid, general properties of the field-free alignment are revisited by comparing gaseous p-H2 with N2. The interplay between the polarization direction of the excitation pulses and the axis directionality of the crystal is shown to affect the alignment dynamics via the spatial (M =0, ±1, ±2) composition of the roton wave packets. We simulate experimental traces by incorporating the induced alignment degree in the calculation of heterodyne-detected realization of femtosecond pump-probe optical Kerr effect spectroscopy. With the help of dispersed, two-dimensional resolved images of the calculated signal we reproduce the experiment as a whole. To that end, the effects of probe chirp, shape, and power must be explored in detail. We find good agreement with previous experiments and unravel the ambiguity of tracing back the wave-packet composition from the signal; in particular, we find that the effect of quantum phase factors of all the components should be taken into account when explaining the signal properties. [ABSTRACT FROM AUTHOR]

Photodynamics calculations of a ClF molecule in solid Ar are compared to experimental results and a new interpretation is given for the observed femtosecond-pump–probe signal modulation. We analyze the round-trip and depolarization times for the excited state wave-packet motion and discuss the incorporation of lattice cage motions that partially explain the time dependence of the measured signal. Librational eigenstates and eigenenergies are calculated by solving the rotational Schrödinger equation in the previously computed [T. Kiljunen, M. Bargheer, M. Gühr and N. Schwentner, Phys. Chem. Chem. Phys., 2004, 6, 2185–2197] octahedral potentials that hinder free molecular rotation in the solids. The obtained level structure is compared to infrared-spectroscopic results. We comment on the correspondence between temperature effects in the classical dynamics of the nuclei and the quantum mechanical probability distributions. We find the combinative treatment of different simulation temperatures congruous for interpreting the experimental results at cryogenic conditions.

Molecular alignment by a strong nonresonant laser pulse and a subsequent ultrafast pump–probe experiment are investigated by classical molecular dynamics simulations. A tendency to molecular alignment in the solid host in the presence of an intense ultrashort laser field is examined by simulating the external force due to the polarizability - field interaction. The ground state rotational potential of the ClF molecule is evaluated as the key determining factor along with the dynamics. The pump–probe scheme consists of time-delayed excitations X 1Σ0 → B 3Π0or 1Π1 → ionic states of ClF molecule in Ar or Kr crystals. We show the yields of dissociating ClF trajectories and discuss the fate of cage-exiting F atoms as a competing event to geminate recombination. Emphasis is put on the recombining trajectories. We extract the round-trip times and reorientations for the excited state “wave-packet” motion as important parameters for the analysis of the experimental photodynamics, and show the surrounding lattice response to the collisions.