Sol–Gel Approach for Design of Pt/Al2O3-TiO2 System—Synthesis and Catalytic Tests

Al2O3-TiO2 systems with Ti:Al 0.1, 0.5 and 1.0 molar ratio obtained by the sol–gel method have been used as a platinum support. As a precursor of alumina gel, aluminum isopropoxide has been chosen. Titanium tert-butoxylate was applied to obtain titania gel and hexachloroplatinic acid was applied as a source of platinum. The systems have been characterized by the following methods: thermogravimetric analysis (TGA), Fourier transformation infrared spectroscopy (FTIR), X-ray powder diffraction (XRPD), low-temperature nitrogen adsorption–desorption isotherms (BET, BJH), temperature-programmed reduction with hydrogen (TPR-H2) and hydrogen chemisorption. Reactions of toluene to methylcyclohexane and selective o-chloronitrobenzene (o-CNB) to o-chloroaniline (o-CAN) hydrogenation were used as the tests of systems’ catalytic activity. The application of Al2O3-TiO2 as a support has enabled the obtaining of platinum catalysts showing high activities for hydrogenation of toluene and selective hydrogenation of o-chloronitrobenzene to o-chloroaniline in the liquid phase. The highest activity in both reactions has been found for Pt/Al2O3-0.5TiO2 catalyst and the highest selectivity for Pt/Al2O3-. The activity of Pt/Al2O3-TiO2 catalysts was higher than that of alumina-supported ones.

Synergistic Effect of FeNi Bimetallic Clusters for the Catalytic of Hydrogen Dissociation and Desorption: A Density Functional Theory Study

Cognition to the metal-metal interactions is of vital importance for the catalytic process and would help exploring novel catalysts. In the present study, the model system of FexNiy (x + y = 6) bimetallic clusters was utilized to study how metal-metal interactions influence the catalytic performance. The formation energies of different FeNi clusters, the hydrogen chemisorption energies together with the maximum hydrogen capacity and the saturated hydrogen atoms desorption energies were calculated. Bimetallic clusters exhibit a superior performance than pure clusters. Especially, Fe2Ni4 cluster has the highest hydrogen loading capacity, the most facile hydrogen molecule dissociation activation energy barrier and the lowest hydrogen atom desorption energy, suggesting that it is easier to dissociate H2 and release the H atoms. As a consequence, by adjusting appropriate metal/metal ratios, it is possible to design bimetallic catalysts with excellent catalytic performance.

Bimetallic Ni–Ru and Ni–Re Catalysts for Dry Reforming of Methane: Understanding the Synergies of the Selected Promoters

Designing an economically viable catalyst that maintains high catalytic activity and stability is the key to unlock dry reforming of methane (DRM) as a primary strategy for biogas valorization. Ni/Al2O3 catalysts have been widely used for this purpose; however, several modifications have been reported in the last years in order to prevent coke deposition and deactivation of the samples. Modification of the acidity of the support and the addition of noble metal promoters are between the most reported strategies. Nevertheless, in the task of designing an active and stable catalyst for DRM, the selection of an appropriate noble metal promoter is turning more challenging owing to the lack of homogeneity of the different studies. Therefore, this research aims to compare Ru (0.50 and 2.0%) and Re (0.50 and 2.0%) as noble metal promoters for a Ni/MgAl2O4 catalyst under the same synthesis and reaction conditions. Catalysts were characterized by XRF, BET, XRD, TPR, hydrogen chemisorption (H2-TPD), and dry reforming reaction tests. Results show that both promoters increase Ni reducibility and dispersion. However, Ru seems a better promoter for DRM since 0.50% of Ru increases the catalytic activity in 10% and leads to less coke deposition.

Sorption of molecular hydrogen on the graphene-like matrix doped by N- and B-atoms

The regularities of interaction of hydrogen molecules with graphene-like planes, where two carbon atoms are replaced by nitrogen or boron atoms, have been studied by the methods of quantum chemistry (DFT, B3LYP, 6-31G**). To take into account the dispersion contributions to the energy of formation of intermolecular complexes that occur during the formation of adsorption supramolecular structures, Grimme’ dispersion correction is used - D3. To study the effect of the size of a graphene-like cluster on the energy of molecular hydrogen chemisorption, polyaromatic molecules (PAM) are used of pyrene, coronene and that consisting of 54 carbon atoms, as well as their nitrogen- and boron-containing analogues where N- and B-atoms are placed in a para-position relative to each other, in the so-called piperazine configuration. The insertion of a heteroatom changes the structure of the transition state and the mechanism of chemisorption. An analysis of the results of quantum chemical calculations showed the highest exothermic dissociative adsorption of the H2 molecule on B-containing graphene-like ones. For N-containing PAM, the exothermicity of the mentioned reaction is somewhat lower, for it a possibility of desorption of atomic hydrogen desorption the surface of the latter with subsequent recombination in the gas phase has been also shown. At the same time, for models of pure graphene-like layer, the data obtained indicate the impossibility of chemisorption of molecular hydrogen. Without a complete analysis of the results for all the possible locations of the pair of hydrogen atoms (formed due to dissociation of the H2 molecule) bound by nitrogen-containing polyaromatic molecules, it can be noted that the dissociative chemisorption of the H2 molecule, regardless of the nature of heteroatom in the PAM, is thermodynamically more probable at the periphery of the model molecules than that in their centers.

Reversible writing/deleting of magnetic skyrmions through hydrogen adsorption/desorption

Magnetic skyrmions are topologically nontrivial spin textures with envisioned applications in energy-efficient magnetic information storage. Toggling the presence of magnetic skyrmions via writing/deleting processes is essential for spintronics applications, which usually require the application of a magnetic or electric field or an electric current. Here we demonstrate the reversible field-free writing/deleting of skyrmions at room temperature, via hydrogen chemisorption/desorption on the surface of Ni and Co films. Supported by Monte-Carlo simulations, the skyrmion creation/annihilation is attributed to the hydrogen-induced magnetic anisotropy change on ferromagnetic surfaces. We also demonstrate the role of hydrogen and oxygen on magnetic anisotropy and skyrmion deletion on other magnetic surfaces. Our results open up new possibilities for designing skyrmionic and magneto-ionic devices.

Room-Temperature Hydrogen-Sensing Capabilities of Pt-SnO2 and Pt-ZnO Composite Nanoceramics Occur via Two Different Mechanisms

Impressive room-temperature gas-sensing capabilities have been reported for nanomaterials of many metal oxides, including SnO2, ZnO, TiO2, WO3, and Fe2O3, while little attention has been paid to the intrinsic difference among them. Pt-SnO2 and Pt-ZnO composite nanoceramics have been prepared through convenient pressing and sintering. The former shows strong and stable responses to hydrogen in 20% O2-N2 (synthetic air) at room temperature, while the responses to hydrogen in N2 cannot be stabilized in limited times; the latter shows strong and stable responses to hydrogen in N2, while the responses to hydrogen in synthetic air are greatly depressed. Further analyses reveal that for Pt-ZnO, the responses result from the reaction between hydrogen and oxygen chemisorbed on ZnO; while for Pt-SnO2, the responses result from two reactions of hydrogen, one is that with oxygen chemisorbed on SnO2 and the other is hydrogen chemisorption on SnO2. These results reveal two different room-temperature hydrogen-sensing mechanisms among MOXs, which results in highly contrasting room-temperature hydrogen-sensing capabilities attractive for sensing hydrogen in oxygen-contained and oxygen-free environments, separately.

Novel hydrogen chemisorption properties of amorphous ceramic compounds consisting of p-block elements: exploring Lewis acid-base Al–N pair site formed in-situ within polymer-derived silicon-aluminum-nitrogen-based system

This paper reports on the relationship between the H2 chemisorption properties and reversible structural reorientation of the possible active site around Al formed in-situ within polymer-derived ceramics (PDCs) based on...

APPLICABILITY OF THE LANGMUIR-HINSHELWOOD MODEL TO HYDROGENATION OF MONO - AND DISACCHARIDES ON THE Ru/HPS MN 100 CATALYST

В данной статье представлены данные по физико-химическому исследованию гетерогенного рутений содержащего катализатора Ru/СПС MN 100. Представлена важность таких исследование для изучения каталитических реакций, для установления возможного механизма реакции гидрирования, а так же как дополнения при кинетических исследованиях. В статье катализатор исследован методом низкотемпературной адсорбции азота, хемосорбции водорода, просвечивающей электронной микроскопии (ПЭМ) и рентгенофотоэлектронной спектроскопии (РФЭС). Метод низкотемпературной адсорбции азота позволил установить, что катализатор характеризуется развитой внутренней удельной поверхностью (726 м/г по модели БЭТ) и характеризуется значительной мезопористостью, при этом наибольший диаметр пор составляет около 3.6 нм. Удельная площадь поверхности активного металла - Ru, по данным метода хемосорбции водорода, составляет 1 м/г. Рутений содержащие частицы распределены по всему объему носителя, при этом они способны образовывать небольшие агрегаты и характеризуются различной степенью кристалличности. Установлен элементный состав поверхности катализатора; Ru имеет различные степени окисления. На основании полученной ранее математическая модель процесса и проведенных физико-химических исследований катализатора предположена модель Ленгмюра-Хиншельвуда для описания механизма реакции жидкофазного каталитического гидрирования моно- и дисахаридов. This article presents data on the physical and chemical study of heterogeneous ruthenium-containing catalyst Ru/SPS MN 100. The importance of such studies for the study of catalytic reactions, for establishing the possible mechanism of the hydrogenation reaction, as well as additions in kinetic studies is presented. In this paper, the catalyst was studied by low-temperature nitrogen adsorption, hydrogen chemisorption, transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS). The method of low-temperature nitrogen adsorption allowed us to establish that the catalyst is characterized by a developed internal specific surface (726 m/g according to the BET model) and is characterized by significant mesoporicity, with the largest pore diameter of about 3.6 nm. The specific surface area of the active metal - Ru, according to the method of hydrogen chemisorption, is 1 m/g. Ruthenium containing particles are distributed over the entire volume of the carrier, while they are able to form small aggregates and are characterized by different degrees of crystallinity. The elemental composition of the catalyst surface has been determined; Ru has different oxidation States. Based on the previously obtained mathematical model of the process and physical and chemical studies of the catalyst, the Langmuir-Hinshelwood model is proposed to describe the reaction mechanism of liquid-phase catalytic hydrogenation of mono - and disaccharides.