Characterizing Adsorption Sites on Ag/SSZ-13 Zeolites: Experimental Observations and Bayesian Inference

Abstract

Three potential adsorption sites within the Ag/SSZ-13 zeolite are compared for their ethylene and water adsorption capacity. Ethylene acts as a model hydrocarbon molecule in this work to stand in for vehicle exhaust, as Ag/SSZ-13 is a candidate material for trapping vehicle emissions during cold-start. Water is also present in vehicle exhaust and competes for adsorption sites with ethylene. The three active sites studied are the intended Ag ion-exchanged with an H in the zeolite framework, an H site (known as a Brønsted acid site) and Ag2O which may form as a nonzeolite adsorption site during the Ag ion-exchange synthesis. Density functional theory (DFT) calculations are conducted using the BEEF-vdw functional for up to two molecules of ethylene and/or water adsorbed per site. A microkinetic model parametrized by the DFT predicts the ethylene adsorption capacity for shifting ethylene feed gas concentrations at 100 °C in the presence of 6% water. Experimental observations are taken at matching conditions as microkinetic model simulations. The DFT energies and their uncertainties for each adsorption site are updated from experiments using a Bayesian statistical framework. The Ag ion and Ag2O sites adsorb more ethylene relative to the Brønsted acid site. The Ag ion and Brønsted acid sites adsorb more water relative to Ag2O.

Investigation of Potential Catalytic Active Sites of Pd/SSZ-13: A DFT Perspective

“…All DFT calculations are spin-polarized calculations. Vibrational analysis was done to obtain zero-point vibrational energy (ZPVE) corrections and vibrational entropy contributions using vtst tools. − The plane wave energy cutoff was 400 eV. A single gamma k -point was used.…”

How a Quantum Computer Could Quantify Uncertainty in Microkinetic Models

“…Adsorption and desorption rate constants were obtained from collision theory. Vibrational entropies of adsorbates were obtained from frequency calculations, 25,26 and full entropies of gas molecules 27 were obtained from the National Institute of Standards and Technology chemistry webbook. 28,29 Table 1 lists the free energies of key reaction steps with uncertainty quantification as calculated by BEEF-vdW.…”

How a Quantum Computer Could Solve a Microkinetic Model

“…QFT (and subsequent gates) will be applied to register r. The choice of the number of qubits in the register is based upon the accuracy with which the eigenvalues may be determined. That is, 4 qubits can determine eigenvalues of 2 4 = 16 values at equal intervals between 0 and 1. Therefore, the eigenvalues may be…”

“…Microkinetic models, a widespread approach to solving chemical kinetics problems, are a communicating channel between the molecular mechanism of a reaction and the reactor behavior . Microkinetic models often take the form of a set of nonlinear, coupled ordinary differential equations and/or Bayesian updates. − Solvable on classical computers, they are the slowest step when performing Monte Carlo simulations to perform uncertainty quantification studies. Furthermore, when systems of equations become large, , and when a large parameter space is explored, the slow-down represented by solving many large microkinetic models can be significant.…”