Theory as a driving force to understand reactions on nanoparticles: general discussion

International audienc

Two-Step One-Pot Reductive Amination of Furanic Aldehydes Using CuAlOx Catalyst in a Flow Reactor

Aminomethylhydroxymethylfuran derivatives are well known compounds which are used in the pharmaceutical industry. Reductive amination of 5-hydroxymethylfurfural (HMF) derived from available non-edible lignocellulosic biomass is an attractive method for the synthesis of this class of compounds. In the present study, the synthesis of N-substituted 5-(hydroxymethyl)-2-furfuryl amines and 5-(acetoxymethyl)-2-furfuryl amines was performed by two-step process, which includes the condensation of furanic aldehydes (HMF and 5-acetoxymethylfurfural) with primary amines in methanol on the first step and the reduction of obtained imines with hydrogen in a flow reactor over CuAlOx catalyst derived from layered double hydroxide on the second step. This process does not require isolation and purification of intermediate imines and can be used to synthesize a number of aminomethylhydroxymethylfurans in good to excellent yield

Three-way catalysis with bimetallic supported Pd-Au catalysts: Gold as a poison and as a promotor

Three-way catalysts containing Au and/or Pd supported on either CeZrOx (CZ) or La$_2$O$_3$/Al$_2$O$_3$ (LA) were studied with respect to their performance in a model feed and characterized by various techniques (physisorption, CO chemisorption, TEM, XRD, XPS, XANES). A drastic support influence was found in both catalytic behavior and Pd-Au relation. While Au was a strong poison for all catalytic functions of Pd (oxidation, NO reduction) on LA, poisoning was much mitigated on CZ, rendering all Pd containing catalysts superior to a commercial reference. After ageing, the poisoning by Au was aggravated on LA. On CZ, Pd-rich bimetallic combinations retained better activity than Pd/CZ, which still outperformed the reference. As Au did not significantly contribute to propene oxidation and NO reduction, activity of Pd was markedly increased under a promoting influence of Au. Stabilization of Pd$^{II}$ by ceria and delayed Pd-Au alloy formation are key features in the CZ-supported PdAu catalysts

Mechanistic Study of Methanol Decomposition and Oxidation on Pt(111)

Decomposition and oxidation of methanol on Pt(111) have been examined between 300 and 650 K in the millibar pressure range using in situ ambient-pressure X-ray photoelectron spectroscopy (XPS) and temperature-programmed reaction spectroscopy (TPRS). It was found that even in the presence of oxygen, the methanol decomposition on platinum proceeds through two competitive routes: fast dehydrogenation to CO and slow decomposition via the C–O bond scission. The rate of the second route is significant in the millibar pressure range, which leads to a blocking of the platinum surface by carbon and to the prevention of further methanol conversion. As a result, without oxygen, the activity of Pt(111) converted to a turnover frequency is ∼0.3 s^–1 at 650 K. The activity strongly increases with oxygen content, achieving 20 s^–1 in an oxygen-rich mixture. The main products of methanol oxidation were CO, CO₂, H₂, and H₂O. The CO selectivity as well as the H₂ selectivity decrease with the increase in oxygen content. It means that the main reaction route is the methanol dehydrogenation to CO and hydrogen; however, in the presence of oxygen, CO oxidizes to CO₂ and hydrogen oxidizes to water. At room temperature, the C1s spectra contain weak features of formate species. This finding points out that the “non-CO-involved” pathway of methanol oxidation realizes on platinum as well. However, the TPRS data indicate that at least under the oxygen-deficient conditions the methanol dehydrogenation pathway dominates. A detailed reaction mechanism of the decomposition and oxidation of methanol agreeing with XPS and TPRS data is discussed