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

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

Theoretical Study of the Methanol Dehydrogenation on Platinum Nanocluster

Методом функционала плотности изучена реакция дегидрирования метанола по механизму разрыва O-H-связи на нанокластере платины Pt79, проведено сравнение с идеальной поверхностью Pt(111). Найдено, что наиболее устойчивые комплексы образуются при адсорбции COНх (x = 1-4) частиц на низкокоординированных атомах нанокластера Pt79, при этом такой предпочтительности для атомов Н не обнаружено. Абсолютные значения энергии адсорбции на вершинах и ребрах нанокластера Pt79 выше на 0,2–0,7 эВ, чем на высококоординированных центрах регулярной поверхности Pt(111). Стабильность адсорбционных комплексов на поверхности нанокластера уменьшается от вершин к ребрам и затем к центру граней (111) нанокластера. Анализ энергетического профиля реакции показывает, что тепловой эффект образования ключевого интермедиата CH3O на кластере Pt79 становится нулевым в отличие от эндотермического (0,5 эВ) на регулярной поверхности Pt(111). Экзотермический эффект всех остальных реакционных стадий, за исключением десорбции СО, на нанокластере увеличивается на ~0,2-0,5 эВThe methanol dehydrogenation through the initial breaking of the O-H bond at Pt79 nanoparticle was studied with the DFT method. The comparison with an ideal surface of Pt (111) was carried out. The most stable complexes were found for COНх (x = 1-4) species adsorbed at low-coordinated atoms of nanocluster Pt79, whereas no preference for adsorption at corners and edges for Н atoms was found. The absolute adsorption energies of COНх species at corner and edge sites of platinum nanocluster increased by 0.2–0.7 eV in comparison with high-coordinated sites of the regular Pt(111) surface. The stabilization effect of adsorption at the nanoparticle decreases from corners to edges and then to the center of (111) facet. According to the reaction energy profile, the thermal effect of the formation of CH3O at the nanocluster becomes close to zero, in contrast to the endothermic effect (0.5 eV) on the regular Pt(111) surface. The exothermic effects for other reaction stages at the platinum nanocluster, excluding CO desorption, increase by ~0.2-0.5 e

XPS Study of Stability and Reactivity of Oxidized Pt Nanoparticles Supported on TiO₂

The method of X-ray photoelectron spectroscopy was used to study the interaction of the model Pt/TiO₂ catalysts with NO₂ and the following reduction of the oxidized Pt nanoparticles in vacuum, hydrogen, and methane. It was shown that, while interacting with NO₂ at room temperature, the metal Pt nanoparticles transform, first, into the phase which was tentatively assigned as particles containing subsurface/dissolved oxygen [Pt-O_sub], and then, into the PtO and PtO₂ oxides. If only the first state of platinum [Pt-O_sub] is formed, it demonstrates exclusively high reactivity toward hydrogen. For the samples containing simultaneously [Pt-O_sub], PtO, and PtO₂, the highest reaction ability was demonstrated by PtO₂; contrary to the other two oxidized states, it is reducing while kept in vacuum under X-ray irradiation. All three coexisting states of the oxidized platinum can be reduced when heated in vacuum as well as while interacting with hydrogen at room temperature. First, PtO₂ is reduced to PtO. PtO and [Pt-O_sub] begin being reduced after the complete consumption of PtO₂. We propose that, when a sample contains simultaneously all three states of oxidized platinum, the supported particles have a core–shell structure with a nucleus of perturbed platinum containing oxygen atoms, which are covered with a film of Pt oxides. It was shown that none of the oxidized states of platinum react with methane at room temperature