The adsorption of benzene on Pt(111) was analyzed using first-principles density functional theoretical cluster and periodic slab calculations. The preferred adsorption site at low coverage is the bridge(30) site with an adsorption energy of 117 kJ/mol. At the bridge(30) site, two of the C p z orbitals are well aligned for overlap with the metal d z 2 and d yz orbitals, leading to a strong C−Pt bond and a strong adsorption energy. The molecule's second important site is the hollow(0) site with an adsorption energy of 75 kJ/mol. Comparing calculated and experimental vibrational frequencies confirms the preference for the bridge site at low coverage and also indicates that adsorption at the hollow(0) site becomes preferred at higher coverage. Adsorption at the hollow(30), the bridge(0) and at the atop sites was found to be unfavorable.

An experimental study of the coking tendency of nine different materials was carried out in a quartz electrobalance setup with a jet stirred reactor (JSR) under industrially relevant ethane steam cracking conditions: T material = 1159 K, P tot = 0.1 MPa, χ ethane = 73%, dilution δ = 0.33 kg H2O /kg HC . A strong influence of the composition of the materials on the coking rate as a function of time on-stream was observed. The initial coking rate varied from 5SEM and EDX analyses of coked and uncoked coupons revealed that the composition of the oxide layer in contact with the cracked gas, formed after the initial preoxidation or decoking, has an important influence on the amount of coke deposited. Materials that formed a thin Al 2 O 3 layer on the coupon surface showed a higher coking resistance. A uniform surface composition and a high resistance to spalling and fractures are other important characteristics of good materials.

To account for thermal and entropic effects caused by the dynamics of the motion of the reaction intermediates, ethanol adsorption on the Brønsted acid site of the H-ZSM-5 catalyst has been studied at different temperatures and ethanol loadings using ab initio molecular dynamics (AIMD) simulations, infrared (IR) spectroscopy, and calorimetric measurements. At low temperatures (T ≤ 400 K) and ethanol loading, a single ethanol molecule adsorbed in H-ZSM-5 forms a Zundel-like structure where the proton is equally shared between the oxygen of the zeolite and the oxygen of the alcohol. At higher ethanol loading, a second ethanol molecule helps to stabilize the protonated ethanol at all temperatures by acting as a solvating agent. The vibrational density of states (VDOS), as calculated from the AIMD simulations, are in excellent agreement with measured IR spectra for C 2 H 5 OH, C 2 H 5 OD, and C 2 D 5 OH isotopomers and support the existence of both monomers and dimers. A quasi-harmonic approximation (QHA), applied to the VDOS obtained from the AIMD simulations, provides estimates of adsorption free energy within ∼10 kJ/mol of the experimentally determined quantities, whereas the traditional approach, employing harmonic frequencies from a single ground state minimum, strongly overestimates the adsorption free energy by at least 20∼50 kJ/mol. This discrepancy is traced back to the inability of the harmonic approximation to represent the contributions to the vibrational motions of the ethanol molecule upon confinement in the zeolite.

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