Critical Step in the HCl Oxidation Reaction over Single-Crystalline CeO_2–<i>x</i>(111): Peroxo-Induced Site Change of Strongly Adsorbed Surface Chlorine

The catalytic oxidation of HCl by molecular oxygen (Deacon process) over ceria allows the recovery of molecular chlorine from the omnipresent HCl waste produced in various industrial processes. In previous density functional theory (DFT) model-calculations by Amrute et al. [J. Catal. 2012, 286, 287−297.], it was proposed that the most critical reaction step in this process is the displacement of tightly bound chlorine at a vacant oxygen position on the CeO2(111) surface (Clvac) toward a less strongly bound cerium on-top (Cltop) position. This step is highly endothermic by more than 2 eV. On the basis of a dedicated model study, namely the reoxidation of a chlorinated single-crystalline Clvac-CeO2–x(111)-(3 × 3)­R30° surface structure, we provide in situ synchrotron-based spectroscopic data (high resolution core level spectroscopy (HRCLS) and X-ray adsorption near edge structure (XANES)) for this oxygen-induced dechlorination process. Combined with theoretical evidence from DFT calculations, the Clvac → Cltop displacement reaction is predicted to be induced by an adsorbed peroxo species (O22–), making the displacement step concerted and exothermic by 0.6 eV with an activation barrier of only 1.04 eV. The peroxo species is shown to be important for the reoxidation of Clvac-CeO2–x(111) and is considered essential for understanding the function of ceria in oxidation catalysis

Critical Step in the HCl Oxidation Reaction over Single-Crystalline CeO_2–<i>x</i>(111): Peroxo-Induced Site Change of Strongly Adsorbed Surface Chlorine

The catalytic oxidation of HCl by molecular oxygen (Deacon process) over ceria allows the recovery of molecular chlorine from the omnipresent HCl waste produced in various industrial processes. In previous density functional theory (DFT) model-calculations by Amrute et al. [J. Catal. 2012, 286, 287−297.], it was proposed that the most critical reaction step in this process is the displacement of tightly bound chlorine at a vacant oxygen position on the CeO2(111) surface (Clvac) toward a less strongly bound cerium on-top (Cltop) position. This step is highly endothermic by more than 2 eV. On the basis of a dedicated model study, namely the reoxidation of a chlorinated single-crystalline Clvac-CeO2–x(111)-(3 × 3)­R30° surface structure, we provide in situ synchrotron-based spectroscopic data (high resolution core level spectroscopy (HRCLS) and X-ray adsorption near edge structure (XANES)) for this oxygen-induced dechlorination process. Combined with theoretical evidence from DFT calculations, the Clvac → Cltop displacement reaction is predicted to be induced by an adsorbed peroxo species (O22–), making the displacement step concerted and exothermic by 0.6 eV with an activation barrier of only 1.04 eV. The peroxo species is shown to be important for the reoxidation of Clvac-CeO2–x(111) and is considered essential for understanding the function of ceria in oxidation catalysis

Tailored Formation of N‑Doped Nanoarchitectures by Diffusion-Controlled on-Surface (Cyclo)Dehydrogenation of Heteroaromatics

Surface-assisted cyclodehydrogenation and dehydrogenative polymerization of polycyclic (hetero)aromatic hydrocarbons (PAH) are among the most important strategies for bottom-up assembly of new nanostructures from their molecular building blocks. Although diverse compounds have been formed in recent years using this methodology, a limited knowledge on the molecular machinery operating at the nanoscale has prevented a rational control of the reaction outcome. We show that the strength of the PAH–substrate interaction rules the competitive reaction pathways (cyclodehydrogenation <i>versus</i> dehydrogenative polymerization). By controlling the diffusion of N-heteroaromatic precursors, the on-surface dehydrogenation can lead to monomolecular triazafullerenes and diazahexabenzocoronenes (N-doped nanographene), to N-doped oligomeric or polymeric networks, or to carbonaceous monolayers. Governing the on-surface dehydrogenation process is a step forward toward the tailored fabrication of molecular 2D nanoarchitectures distinct from graphene and exhibiting new properties of fundamental and technological interest