The study is dedicated to the investigation of the catalytic properties of M3+ 0.33 Ti2(PO4)3 (M - La, Sm, Dy) phosphates in ethanol conversion reactions. The powder samples of the NASICON-type phosphates were synthesized by the Pechini technique. Their phase purity and structure characterization were performed using XRD, IR spectroscopy, SEM, BET and BJH methods. Structural data indicated that the transition from La to Dy was accompanied by a decrease in M - O bond lengths, which is compensated by longer neighboring Ti-O bonds, ultimately leading to greater distortion of the surrounding octahedra. The catalytic activity of M0.33Ti2(PO4)3 (M - La, Sm, Dy) phosphates has been studied in ethanol reforming reactions in the temperature range of 240-400 degrees C. The regularities of changes in the catalytic properties in the La-*Sm-*Dy series have been traced. The selectivity of ethanol conversion was found to depend on the phosphate composition. The best alcohol conversion was achieved on Dy-phosphate at 400 degrees C with an ethylene selectivity of 66 %.

Ceramics of the Na1+2xMxZr2-x(PO4)3 (M - Mg, Mn) composition were synthesized by the co-precipitation technique with subsequent annealing. The samples were characterized using X-ray diffraction with the Rietveld refinement, scanning electron microscopy, and impedance spectroscopy. The studied phosphates belong to the NASICON type structure. The solid solutions (0 <= x <= 1.0) were shown to be formed in the investigated systems. To study the effect of the chemical composition and sintering additive on conductivity, two series of ceramics were prepared for each phosphate: with and without ZnO (2 wt%) additive. The ionic conductivity of the studied phosphates followed the Arrhenius law and passed through a maximum with x growth. It was shown that the addition of zinc oxide also leads to partial substitution of zirconium in the lattice and an increase in ionic conductivity. The highest conductivity was achieved for the Na2.6Mg0.8Zr1.2(PO4)3 ceramic with 2 wt% ZnO additive (6.8 center dot 10-3 S cm-1 at 673 K).

Mineral-like single-phase NZP materials of variable composition M0.5Zr2(AsO4)x(PO4)3 − x (M − Sr, Ba, Cd) are of interest as matrices for isolation of high-level Sr, Ba and Cd wastes generated during reprocessing of irradiated nuclear fuel. Such polycrystalline phases were synthesized by sol-gel method with subsequent heat treatment and investigated by X-ray diffraction, IR spectroscopy and electron-probe microanalysis. Rietveld structure refinement showed that the framework is formed by ZrO6 octahedra and mixed AsO4/PO4 tetrahedra connected by vertices; Sr, Ba or Cd cations are located in extra-framework positions. Arsenate-phosphates can be classified as medium thermal expansion materials due to their average coefficient of linear thermal expansion of 2.8∙10−6 °C−1. Chemical durability test indicates that the leaching rate of Sr2+ ions from the NZP structure type solid solution is of the order of 10−5 g cm−2 d−1.

Phases of variable composition A2-(x)A'xMg0.5Zr1.5(PO4)(3) (AA' - KNa, KRb, KCs, 0 <= x <= 2) with langbeinite and kosnarite structures can serve as matrices immobilizing radioactive waste. They were synthesized by sol-gel method followed by heat treatment and investigated by X-ray diffraction at different temperatures, IR spectroscopy, scanning electron microscopy and electron probe microanalysis. A Rietveld refinement of the KCsMg0.5Zr1.5(PO4)(3) structure showed that the framework is formed by octahedra (Mg/Zr)O-6 and tetrahedra PO4 connected by vertices; potassium and cesium cations are located in cavities. When the temperature changes, phosphates with the langbeinite structure expand uniformly in all directions: alpha, = alpha b = alpha c = (4.2-6.6).10(-6) C- 1, without undergoing polymorphic transitions. Phosphate Na2Mg0.5Zr1.5(PO4)(3), which crystallizes in the kosnarite structure type, expands anisotropically: alpha a = -2.6.10(-6), alpha c = 8.2.10(-6), alpha(av) = 1.0.10(-6) C- 1. The chemical durability test shows that the leaching rate of Cs ions from the solid solution with langbeinite structure is of the order of 10-5 g cm (-2) d(-1).

Министерство науки и высшего образования Российской Федерации Российское химическое общество им.Д.И.Менделеева Секция по химической термодинамике и термохимии Научного совета РАН по физической химии Сибирское Отделение Российской Академии Наук Институт неорганической химии им.А.В.Николаева СО РАН

Министерство науки и высшего образования Российской Федерации Российское химическое общество им.Д.И.Менделеева Секция по химической термодинамике и термохимии Научного совета РАН по физической химии Сибирское Отделение Российской Академии Наук Институт неорганической химии им.А.В.Николаева СО РАН

The manifestations of the Bi1- x Sb x Cr2(PO4)3 system with the α-CaMg2(SO4)3 structure were obtained and characterized by the evaporation of salt solutions with heat treatment. Refinement of the Rietveld method for the structure of BiCr2(PO4)3 ( x = 0) and SbCr2(PO4)3 ( x = 1) showed that the [Cr2(PO4)3]3∞ framework is formed by CrO6 octahedra doubled by faces, PO4 tetrahedra are between the dependences, attached to the octahedrons by oxygen vertices, the voids of the framework are populated by six-coordinated bismuth or antimony atoms. By varying the composition of the Bi1- x Sb x Cr2(PO4)3 solid solution everywhere, it is possible to obtain materials with low thermal expansion coefficients: 0.5×10-6 ≤ α av ≤ 1.9×10-6 °C-1.

Synthesis process, structure and luminescent properties of NASICON (Na super ionic conductor) type phosphates doped with europium have been investigated for the Na1-xEu0.33xTi2(PO4)3 series. The samples were synthesized via Pechini technique. Differential thermal analysis of the reaction mixtures was used to choose the optimal scheme for the thermal treatment of the phosphates. The obtained samples were studied by means of X-ray powder diffraction (including Rietveld structure refinement), Infrared spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. It was shown that the phosphates with 0 ≤ x ≤ 0.1 were crystallized in the space group $$R\overline 3 c$$ , while the phosphates with 0.2 ≤ x ≤ 1.0 characterized by the space group $$R\overline 3$$ . Photoluminescence emission spectra of the phosphates Na1-xEu0.33xTi2(PO4)3 showed typical emission bands of Eu3+ ions, due to 5D0 → 7FJ transitions. The intensity of the emission bands rises with the concentration of europium up to x = 0.7 (Na0.3Eu0.23Ti2(PO4)3), while a further increase of x results into concentration quenching. Na0.5Eu0.167Ti2(PO4)3 structure and Na1-xEu0.33xTi2(PO4)3 photoluminescence emission spectra

The phosphates of the composition Ca0.5+xMxTi2-x(PO4)(3) (M - Ni, Mg) were synthesized by a co-precipitating of salts in aqueous solutions followed by thermal treatment stages. The studied series formed limited NZP solid solutions within the regions 0 <= x <= 0.5 (Ni) and 0 <= x <= 1 (Mg). The Rietveld refinement of the Ca1.2Mg0.7Ti1.3(PO4)(3) structure showed that its basis is framework formed by TiO6 and (Mg/Ti)O-6 octahedra (together with PO4 tetrahedra), and the Ca2+ ions are situated in the cavities. Thermal expansion of the phosphates depending on their chemical composition was characterized in the temperature range from 173 to 473 K. There was a gradual decrease in the linear thermal expansion coefficients with x growth, so that average linear coefficients varied from (11.0-2.6)center dot 10(-6) K-1. Low average thermal expansion coefficient and its low anisotropy allow the studied phosphate ceramics to withstand temperature changes.

The conversion of ethanol towards ethylene and diethyl ether in the presence of catalysts requires special consideration from the perspective of green chemistry. Ethanol dehydration was studied on a complex titanium phosphate MAlTiP (M0.5(1+x)AlxTi2-x(PO4)3 with M = Ni, Mn (x = 0; 0.2)) catalysts, alongside a NASICON-type structure synthesized by the sol–gel method. The initial catalysts were characterized by N2 gas sorption, SEM, XRD and spectroscopic methods (Raman and DRIFT of adsorbed CO and C6H6). The results revealed that all catalysts exhibited high activity and selectivity at 300–420 °C. The conversion of ethanol increases with the reaction temperature, reaching 67–80% at 420 °C. The MnAlTiP exhibited the highest ethylene selectivity among other catalysts, with 87% at 420 °C. The aluminum modification improved the acid properties of the catalysts, due to the appearance of Lewis acid sites (LAS) and the strength moderate Brønsted acid sites (BAS). It was shown that the activity of complex phosphates in ethanol dehydration increases with the strength of the Brønsted acid sites (BAS).

Samples of the Bi 1– x Sb х Cr 2 (PO 4 ) 3 system with the structure of α-CaMg 2 (SO 4 ) 3 were obtained by evaporation of a solution of salts with subsequent heat treatment, and characterized. Refinement of the BiCr 2 (PO 4 ) 3 ( x = 0) and SbCr 2 (PO 4 ) 3 ( x = 1) structures by the Rietveld method showed that the [Cr 2 (PO 4 ) 3 ] 3∞ framework is formed by CrO 6 octahedra doubled by faces, between which PO 4 tetrahedra attached to the octahedra by oxygen vertices are located, the voids of the framework are populated by six coordinated bismuth or antimony atoms. By varying the composition of the unlimited solid solution Bi 1– x Sb х Cr 2 (PO 4 ) 3 , it is possible to obtain materials with low thermal expansion coefficients: 0.5×10 −6 ≤ α av ≤ 1.9×10 −6 °C −1 .

Phosphates Na 1 – x R 0.33 x Ti 2 (PO 4 ) 3 (R = Y or La; 0 ≤ х ≤ 1) were synthesized by the Pechini process and characterized by X-ray diffraction, electron microscopy with microprobe analysis, and IR spectroscopy. The systems exhibit isodimorphism to form a series of solid solutions belonging to the NaZr 2 (PO 4 ) 3 (NZP) structural type and crystallizing in space group R 3̅ c or R 3̅. The Rietveld structural studies confirmed the isomorphic miscibility of sodium and the rare-earth element in the interstices of the NZP structure. The unit cell parameter с in the phosphates studied tends to increase, and the parameter а tends to decrease, in response to rising temperature, which trends are typical of NZP phosphates.

Phosphates Na1 – xR0.33xTi2(PO4)3 (R = Y or La; 0 ≤ х ≤ 1) were synthesized by the Pechini process and characterized by X-ray diffraction, electron microscopy with microprobe analysis, and IR spectroscopy. The systems exhibit isodimorphism to form a series of solid solutions belonging to the NaZr2(PO4)3 (NZP) structural type and crystallizing in space group Rc or RThe Rietveld structural studies confirmed the isomorphic miscibility of sodium and the rare-earth element in the interstices of the NZP structure. The unit cell parameter с in the phosphates studied tends to increase, and the parameter а tends to decrease, in response to rising temperature, which trends are typical of NZP phosphates.

Na1 + 2xZnxZr2 – x(PO4)3 phosphates have been prepared by a sol–gel process followed by heat treatment. A limited series (0 ≤ x ≤ 0.4) of solid solutions with the NASICON structure has been obtained in the system studied. The crystal structure of Na1.8Zn0.4Zr1.6(PO4)3 has been refined by the Rietveld method. The results demonstrate that the structural basis of this phosphate has the form of a mixed framework made up of corner-sharing (Zr/Zn)O6 octahedra and PO4 tetrahedra. The Na+ ions partially occupy two types of structural voids. The sodium ion conductivity of the Na1 + 2xZnxZr2 – x(PO4)3 phosphates has been studied using impedance spectroscopy. Their conductivity has been shown to increase with increasing carrier concentration, reaching 2.7 × 10–4 S/cm at 723 K in the case of Na1.8Zn0.4Zr1.6(PO4)3. It has been shown that increasing the degree of zinc substitution for zirconium leads to a change in the mechanism of defect formation in the materials studied: from intrinsic disorder at x = 0 to impurity-related disorder for x > 0.2. We have estimated the enthalpy of intrinsic sodium ion disorder (72 kJ/mol) and the activation energy for sodium migration (61 kJ/mol).

A method has been developed for the synthesis of single-phase sulfate-phosphates, which provides keeping from sulfur losses by its binding to sulfate with a high decomposition temperature. The thermally stable sulfate-phosphate Pb2Mg2(PO4)2SO4 was studied using X-ray diffraction, IR spectroscopy, DTA, and electron-probe microanalysis. According to the results of the study by the Rietveld method, this compound belongs to the eulytite structural type (space group I4̅3d ). When the temperature changes, its crystals expand isotropically without polymorphic transitions.

M0.5+xMgxZr2–x(PO4)3 (M = Cd, Sr) phosphates have been synthesized via precipitation. In both systems, we have obtained limited solid solutions with the NaZr2(PO4)3 (NZP) structure (in the range 0 ≤ x ≤ 0.6 for M = Cd and 0 ≤ x ≤ 0.5 for M = Sr). Structure refinement of SrMg0.5Zr1.5(PO4)3 by the Rietveld method has shown that the Zr4+ and Mg2+ cations reside on framework sites, whereas Sr2+ ions occupy structural voids. The thermal expansion of the M0.5+xMgxZr2–x(PO4)3 (M = Cd, Sr) phosphates has been studied by X-ray diffraction in the temperature range 173–473 K. The results demonstrate that the incorporation of the larger (Sr2+) cations into voids in the NZP structure leads to a decrease in the magnitude of the axial linear thermal expansion coefficients. We have predicted and investigated a solid solution, Sr0.7Mg0.2Zr1.8(PO4)3, with a nearly zero thermal expansion anisotropy (0.55 × 10–6 K–1) and a small average thermal expansion coefficient (3.92 × 10–6 K–1).