An Ab Initio embedded cluster study of the adsorption of NH3 and NH4+ in chabazite

The adsorption of NH3 in acidic zeolites has been studied extensively experimentally. Therefore, it can be used very well to verify a model used in a quantum chemical calculation. Here, we present a calculation that, from a quantum chemical point of view, should give a reliable description of the adsorption process. We studied the adsorption of NH3 and NH4+ in chabazite with the embedded cluster method using a reasonable basis set, applying the counterpoise correction and including electron correlation. The geometry was partially optimized. With this calculation we verified the reliability of our model and obtained information that cannot be obtained experimentally. The adsorption energies of hydrogen-bonding NH3 and of NH4+ were -70 +/- 10 kJ/mol and -120 +/- 15 kJ/mol, respectively. The latter value compares very well with the experimental heat of adsorption. NH4+ has a high coordination with the zeolite wall; this is confirmed experimentally. A good geometry is obtained if the boundary of the embedded cluster is kept fixed to that of the zeolite crysta

Interaction of ammonia with a zeolitic proton: ab initio quantum-chemical cluster calculations

The interaction of NH3 and a zeolitic cluster as well as the protonation of NH3 by zeolitic protons were studied by quantum-chem. calcns. on small clusters at different levels of approxn. The focus was on a comparison of results obtained by the different methods. The clusters were studied at the SCF level as well as at the correlated level. Electron correlation is included through second-order Moeller-Plesset perturbation theory. The basis-set superposition error (BSSE) was avoided by using the counterpoise scheme. Monodentate singly bonded NH3 (NH3 attached to 1 O atom) forms a strong H bond with the zeolitic OH group. This bond has a strength of 60 or 67 kJ/mol, depending on the geometry of the zeolitic cluster. This value is approx. half the exptl. heat of desorption. For this case, the O-N distance is very short (2.74 or 2.73 .ANG.) and the intermol. O-H-N stretching frequency is calcd. to be 185 or 193 cm-1. The latter values agree reasonably with exptl. data. Upon complexation with NH3 and OH stretching frequency shows a red shift of 551 cm-1. Proton transfer from the zeolitic cluster to NH3 is calcd. to be unfavorable by 52 kJ/mol, as long as NH4+ is considered to be monodentate coordinated. The description of the H bonded form is only slightly dependent on the basis set used. However, the proton-transfer energy does depend strongly on the basis set used. Electron correlation makes the proton transfer more favorable. The BSSE has a large influence on the description of the structures, esp. if electron correlation is included. Although electron correlation has a non negligible effect on the proton-transfer energy, some conclusions can be drawn from SCF calcns. on doubly and triply coordinated NH4+. The calcd., energy of adsorption now is approx. twice that calcd. for the H bonded and singly coordinated NH3 and close to exptl. obsd. values of NH3 adsorption. These results indicate that these adsorption modes are prefered over the singly bonded form. These forms are preferred because of the favorable electrostatic stabilization of NH4+ when bonded to the cluster by 2 or 3 H bond

Spectroscopy, energetics and siting of NH+4 in zeolites; theory and experiment

The adsorption of an NH3 mol. on an acidic zeolite and the proton transfer from the zeolite to the NH3 are studied by quantum chem. methods. The NH+4 is adsorbed with 2 or 3 H bonds to the zeolite. The calcd. vibrational frequencies explain the exptl. IR spectra. [on SciFinder (R)

Lattice-relaxation of zeolites

Quantum-chemical cluster calculations as well as solid-state chemical lattice-calculations indicate that zeolitic SiO2- and AlPO4-structures are flexible structures. The structures reflect the subtle balance of electrostatic and covalent interactions. The different electrostatic interactions lower the symmetry of layered AlPO4-structures compared to that of the corresponding SiO2-compounds. The result is a smaller zeolite-channel dimension for the AlPO4-structure compared to that of the corresponding SiO2-network. Deprotonation of the zeolite-lattice leads to large local changes in geometry that changes acidity compared to that predicted for a non-flexible lattice. Changes in lattice vibrational frequencies are consistent with the theoretically predicted relaxation of the zeolite-lattic

Autoantibodies against type I IFNs in patients with life-threatening COVID-19

Interindividual clinical variability in the course of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is vast. We report that at least 101 of 987 patients with life-threatening coronavirus disease 2019 (COVID-19) pneumonia had neutralizing immunoglobulin G (IgG) autoantibodies (auto-Abs) against interferon-w (IFN-w) (13 patients), against the 13 types of IFN-a (36), or against both (52) at the onset of critical disease; a few also had auto-Abs against the other three type I IFNs. The auto-Abs neutralize the ability of the corresponding type I IFNs to block SARS-CoV-2 infection in vitro. These auto-Abs were not found in 663 individuals with asymptomatic or mild SARS-CoV-2 infection and were present in only 4 of 1227 healthy individuals. Patients with auto-Abs were aged 25 to 87 years and 95 of the 101 were men. A B cell autoimmune phenocopy of inborn errors of type I IFN immunity accounts for life-threatening COVID-19 pneumonia in at least 2.6% of women and 12.5% of men

Nonlinearity and Least-Squares.

Since almost all functional relations in our geodetic models are nonlinear, it is important, especially from a statistical inference point of view, to know how nonlinearity manifests itself at the various stages of an adjustment. In this paper particular attention is given to the effect of nonlinearity on the first two moments of least squares estimators. Expressions for the moments of least squares estimators of parameters, residuals and functions derived from parameters, are given. The measures of nonlinearity are discussed both from a statistical and differential geometric point of view. Finally, our results are applied to the 2D symmetric Helmert transformation with a rotational invariant covariance structure

An Ab Initio embedded cluster study of the adsorption of NH3 and NH4+ in chabazite

The adsorption of NH3 in acidic zeolites has been studied extensively experimentally. Therefore, it can be used very well to verify a model used in a quantum chemical calculation. Here, we present a calculation that, from a quantum chemical point of view, should give a reliable description of the adsorption process. We studied the adsorption of NH3 and NH4+ in chabazite with the embedded cluster method using a reasonable basis set, applying the counterpoise correction and including electron correlation. The geometry was partially optimized. With this calculation we verified the reliability of our model and obtained information that cannot be obtained experimentally. The adsorption energies of hydrogen-bonding NH3 and of NH4+ were -70 +/- 10 kJ/mol and -120 +/- 15 kJ/mol, respectively. The latter value compares very well with the experimental heat of adsorption. NH4+ has a high coordination with the zeolite wall; this is confirmed experimentally. A good geometry is obtained if the boundary of the embedded cluster is kept fixed to that of the zeolite crysta