35 research outputs found
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<sup>–1</sup> at 650 K. The activity strongly increases with oxygen content, achieving
20 s<sup>–1</sup> in an oxygen-rich mixture. The main products
of methanol oxidation were CO, CO<sub>2</sub>, H<sub>2</sub>, and
H<sub>2</sub>O. The CO selectivity as well as the H<sub>2</sub> 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 CO<sub>2</sub> 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
X-ray absorption and photoemission studies of the active oxygen for ethylene epoxidation over silver
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
The model thin film alumina catalyst support suitable for catalysis-oriented surface science studies
XPS Study of Stability and Reactivity of Oxidized Pt Nanoparticles Supported on TiO<sub>2</sub>
The method of X-ray photoelectron
spectroscopy was used to study
the interaction of the model Pt/TiO<sub>2</sub> catalysts with NO<sub>2</sub> and the following reduction of the oxidized Pt nanoparticles
in vacuum, hydrogen, and methane. It was shown that, while interacting
with NO<sub>2</sub> 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>sub</sub>], and then, into the PtO and PtO<sub>2</sub> oxides. If only the
first state of platinum [Pt-O<sub>sub</sub>] is formed, it demonstrates
exclusively high reactivity toward hydrogen. For the samples containing
simultaneously [Pt-O<sub>sub</sub>], PtO, and PtO<sub>2</sub>, the
highest reaction ability was demonstrated by PtO<sub>2</sub>; 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, PtO<sub>2</sub> is reduced
to PtO. PtO and [Pt-O<sub>sub</sub>] begin being reduced after the
complete consumption of PtO<sub>2</sub>. 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
Spatially resolved NMR spectroscopy of heterogeneous gas phase hydrogenation of 1,3-butadiene with parahydrogen
Magnetic resonance-based methods such as nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are widely used to provide in situ/operando information of chemical reactions. However, the low spin density and magnetic field inhomogeneities associated with heterogeneous catalytic systems containing gaseous reactants complicate such studies. Hyperpolarization techniques, in particular parahydrogen-induced polarization (PHIP), increase significantly the NMR signal intensity. In this study, we test 16 glass tube reactors containing Pd, Pt, Rh or Ir nanoparticles dispersed on a thin layer of TiO2, CeO2, SiO2 or Al2O3 for the hydrogenation of 1,3-butadiene using parahydrogen. The catalytic coatings of Ir and Rh gave hydrogenation products with the highest nuclear spin polarization while the coatings of Pd are the most selective ones for the semihydrogenation of 1,3-butadiene to 1- and 2-butenes. Spatially resolved NMR spectroscopy of the reagent and the product distribution along the reactor axis provided further mechanistic insight into the catalytic function of these reactive coatings under operando conditions.ISSN:2044-4753ISSN:2044-476