Evgeny Yu. Gerasimov

Ruthenium Clusters on Carbon Nanofibers for Formic Acid Decomposition: Effect of Doping the Support with Nitrogen

The catalytic properties of 1 wt % Ru catalysts with the same mean Ru cluster size of 1.4–1.5 nm supported on herringbone‐type carbon nanofibers with different N contents were compared for H2 production from formic acid decomposition. The Ru catalyst on the support with 6.8 wt % N gave a 1.5–2 times higher activity for the dehydrogenation reaction (CO2, H2) than the catalyst on the undoped support. The activity in the dehydration reaction (CO, H2O) was the same. As a result, the selectivity to H2 increased significantly from 83 to 92 % with N‐doping, and the activation energies for both reactions were close (55–58 kJ mol−1). The improvement could be explained by the presence of Ru clusters stabilized by pyridinic N located on the open edges of the external surface of the carbon nanofibers. This N may activate formic acid by the formation of an adduct (>NH+HCOO−) followed by its dehydrogenation on the adjacent Ru clusters.

Hydrodeoxygenation of methyl palmitate over sulfided Mo/Al2O3, CoMo/Al2O3 and NiMo/Al2O3 catalysts

The catalytic properties of sulfided Mo/Al2O3, CoMo/Al2O3 and NiMo/Al2O3 catalysts in the hydrodeoxygenation of methyl palmitate as a model compound for triglyceride feedstock were studied at 300 °C and 3.5 MPa in the batch reactor using n-tetradecane, m-xylene and hydrotreated straight-run gas oil (HT-SRGO). The comparison of catalysts performance in n-tetradecane allowed us to see that the sulfided Mo/Al2O3, CoMo/Al2O3 and NiMo/Al2O3 catalysts revealed the same rate of the methyl palmitate conversion but the rate of the intermediate oxygenates conversion decreased in order: CoMoS/Al2O3 > NiMoS/Al2O3 > MoS2/Al2O3. A mixture of linear saturated and unsaturated C15 and C16 hydrocarbons was produced when the oxygenates were fully consumed. The main products obtained over the Mo/Al2O3 and CoMo/Al2O3 catalysts were C16 hydrocarbons (C16/C15 – 16.1 and 2.79, respectively); however, C15 hydrocarbons were preferentially formed over the NiMo/Al2O3 catalyst (C16/C15 – 0.65), highlighting the different contributions of the hydrodeoxygenation (HDO) and decarboxylation/decarbonylation (DeCOx) pathways during the hydroconversion of methyl palmitate over these catalysts. Investigating the solvents influence on the activity of the CoMo/Al2O3 and NiMo/Al2O3 catalysts in the methyl palmitate HDO revealed that the reaction rate was decreased in the following order: n-tetradecane > HT-SRGO > m-xylene. The aromatic compounds did not retard the methyl palmitate transformation, but inhibited the conversion of the intermediate oxygenates. Decreased C16/C15 ratios were observed over both catalysts when m-xylene was used as the reaction medium instead of n-tetradecane.

Strong Metal–Support Interactions for Palladium Supported on TiO2 Catalysts in the Heterogeneous Hydrogenation with Parahydrogen

Parahydrogen‐induced polarization (PHIP) was successfully utilized to demonstrate the strong metal–support interaction (SMSI) effect for palladium supported on titania catalysts. Heterogeneous hydrogenation of 1,3‐butadiene over Pd/TiO2 catalysts led to the formation of 1‐ and 2‐butenes and butane, and hyperpolarized products were obtained if parahydrogen was used in the reaction. However, if the catalysts were reduced in H2 flow at 500 °C before the hydrogenation reaction, the observed polarization levels were significantly lower or even zero, which was indicative of the suppression of the pairwise addition of hydrogen route. This observation indicated the possibility to detect the SMSI effect by the PHIP technique. Moreover, by using X‐ray photoelectron spectroscopy it was shown that Pd is partially present as Pdδ+ after reduction under a hydrogen atmosphere at 500 °C. These results were confirmed by transmission electron microscopy, which revealed the formation of Pdδ+ and the dissolution of Pd in the titania lattice.

Effect of Titania Regular Macroporosity on the Photocatalytic Hydrogen Evolution on Cd1−xZnxS/TiO2 Catalysts under Visible Light

Multiphase photocatalysts Cd1−xZnxS/TiO2 were synthesized through the deposition of solid solutions of cadmium and zinc sulfides on the surface of titania samples with different porous structures, including a 3D‐ordered meso/macroporous structure. The photocatalysts were characterized by a wide range of experimental techniques: X‐ray diffraction, high‐resolution transmission electron microscopy combined with energy‐dispersive X‐ray spectroscopy, N2 adsorption at 77 K, X‐ray photoelectron spectroscopy, and UV/VIS spectroscopy. The photocatalytic activity was tested in a batch reactor for the H2 evolution reaction from aqueous solutions of Na2S/Na2SO3 under visible‐light irradiation (λ=450 nm). The highest achieved photocatalytic activity was 1.8 mmol H2 per gram of photocatalyst per hour. The regular porous structure of titania was demonstrated to enhance the photocatalytic activity and stability of Cd0.4Zn0.6S/TiO2 samples.

Low- and high-temperature oxidation of Mn1.5Al1.5O4 in relation to decomposition mechanism and microstructure

Spinel-like Mn1.5Al1.5O4 is an unstable compound whose decomposition is induced by partial oxidation of Mn2+ ions in the temperature range of 300–800 °C in air. According to XRD, two spinel-like phases, Mn0.4Al2.4O4 and Mn2.8Al0.2O4, are formed during both cooling and heating of Mn1.5Al1.5O4. In this paper, we have studied microstructural changes of Mn1.5Al1.5O4 to understand its decomposition mechanism. During heating, low-temperature oxidation takes place and decomposition proceeds via a nucleation and growth mechanism. As a result slightly Al-doped β-Mn3O4 nanoparticles are formed on the surface of the parent spinel particles. On the contrary, cooling leads to high-temperature oxidation that results preferably in spinodal decomposition and formation of alternating Mn- and Al-rich lamellas of nanosized thickness. The present study provides a fundamental reference for the nanostructure design of a Mn–Al–O system and probably some other ones subjected to oxidative decomposition.

Effect of precursor on the catalytic properties of Ni2P/SiO2 in methyl palmitate hydrodeoxygenation

The effect of phosphorus precursor on the physicochemical and catalytic properties of silica-supported nickel phosphide catalysts in the hydrodeoxygenation (HDO) of aliphatic model compound methyl palmitate (C15H31COOCH3) has been considered. Nickel acetate (Ni(OAc)2) and diammonium hydrogen phosphate ((NH4)2HPO4) (phosphate precursor) or nickel hydroxide (Ni(OH)2) and phosphorous acid (H3PO3) (phosphite precursor) have been used for the catalyst preparation by incipient wetness impregnation of SiO2 with an aqueous solution of the precursors, followed by temperature-programmed reduction in hydrogen flow. Chemical analysis (ICP-AES), H2-TPR, NH3-TPD, 31P MAS NMR, XRD, and TEM have been employed for the characterization of the catalysts. The optimal reduction parameters of the silica-supported nickel phosphide catalysts have been found for the phosphate and phosphite precursors in terms of their activity in methyl palmitate HDO. The Ni2P/SiO2 catalysts prepared by the phosphite method have shown higher catalytic activity in comparison with the Ni2P/SiO2 catalysts prepared by the phosphate method. The activity has been shown to depend on the catalyst handling after reduction: in situ reduced catalysts demonstrate higher conversion of methyl palmitate than the samples exposed to the reduction, passivation and re-reduction steps.

Highly Stable Single-Atom Catalyst with Ionic Pd Active Sites Supported on N-Doped Carbon Nanotubes for Formic Acid Decomposition

Single-atom catalysts with ionic Pd active sites supported on nitrogen-doped carbon nanotubes have been synthesized with a palladium content of 0.2-0.5 wt %. The Pd sites exhibited unexpectedly high stability up to 500 °C in a hydrogen atmosphere which was explained by coordination of the Pd ions by nitrogen-containing fragments of graphene layers. The active sites showed a high rate of gas-phase formic acid decomposition yielding hydrogen. An increase in Pd content was accompanied by the formation of metallic nanoparticles with a size of 1.2-1.4 nm and by a decrease in the catalytic activity. The high stability of the single-atom Pd sites opens possibilities for using such catalysts in high-temperature reactions.

In situ XRD study of Mn-containing oxide catalysts

Mn-containing oxides exhibit high catalytic activity in the reactions of total oxidation of hydrocarbons and CO. It was found that increase in the calcination temperature to 950–1000C lead to the growth of catalytic activity for MnOx-Al2O3 catalysts. In situ XRD studies of MnOx-Al2O3 catalysts shown that active component of the catalysts was formed via decomposition of the hightemperature precursor (cubic spinel Mn3-xAlxO4) followed by the appearance of aggregates consisting of imperfect Mn3O4+δ oxide and amorphous Mn-Al-O phase. The decomposition was accompanied by the formation of weakly bound oxygen which appears to be active in oxidation reactions. The structure of the active component was directly related to the composition of the high-temperature precursor the higher the concentration of manganese cations are in the Mn3-xAlxO4 cubic spinel, the more Mn3O4 and weakly bound oxygen appear in the decomposition product [1]. When Al is replaced by Ga, a significant decrease in catalytic activity is observed. To understand the origin of active component of Mn-containing catalysts, detailed mechanism of high-temperature precursor decomposition was investigated on the model systems – singlephase spinels Mn3-xAlxO4 and Mn3-xGaxO4. In situ XRD analysis indicates that during heating and cooling in the air both spinels decompose at the temperatures range of 400-800oC. This process is accompanied by partially oxidation of Mn2+ to Mn3+ and cation vacancies formation in the spinel structure that leads to decompomposition of initial spinet into two spinel-type phases. Under heating Mn3-xAlxO4 oxide decomposes according to nucleation ang grow mechanism due to the diffusion of Mn cations toward the surface and its segregation into nanoparticles of β-Mn3O4. Spinodal decomposition of initial spinel occurs during cooling caused by Mn3+ clustering. For Mn3xGaxO4 spinel, products of decomposition are different during cooling and heating. Decomposition of Mn3-xGaxO4 leads to formation of two spinel structures with the samilar Mn/Ga ratio but different oxygen content. In situ XRD study shown that difference in catalytic activity in CO oxidation in MnOx-Al2O3 and MnOx-Ga2O3 catalysts is due to different mechanism of precursor decomposition.