Optimization of slurry nebulization inductively-coupled plasma atomic emission spectrometry for the analysis of ZrO2-powder

The optimization and use of ICP-AES with slurry nebulization for the direct analysis of ZrO₂-powder is described. The powder samples are dispersed in water, acidified to pH 2 and the slurry is fed into a Babington nebulizer. The effects of grain size, pH of the suspending medium and standing time on the stability of the slurry are discussed. For the optimization of the ICP operating conditions, a simplex technique is applied and for this purpose three types of objective functions were examined. Identical behaviour of slurries and solutions with the same matrix concentrations in the ICP-AES is achieved for powders with particle sizes lower than 10 m; in the latter case calibration can be performed by standard addition with aqueous solutions. The detection limits for Al, B, Ca, Cu, Fe, Mg, Mn, Na, Ti, V. Y are 0.03 g/g to 10 g/g and the standard deviation is generally lower than 10%. Six commercially available ZrO₂ powders are analyzed by slurry nebulization ICP-AES and the results were found to agree well with those obtained by ICP-AES after chemical decomposition of the samples.On leave from Department of Analytical Chemistry, Technical University, PL-00-664 Warsaw, Poland     

Electroconductivity of Potassium Orthophosphate Modified by Four-Charged Cations

Solid solutions based on K₃PO₄ in systems K_{3 – 4x} E" _x PO₄ (E" = Si, Ti, Ge, Zr, Sn, Hf, Ce) are synthesized. The crystal structure, thermal behavior, and electroconduction of the synthesized solutions is studied. The narrowest single-phase regions take place in the systems where E" = Si, Ge (x 0.025), and the widest, in the system with Zr (x 0.125, at 700°C). Introducing Ti or Sn additives (x 0.05) and minimum quantities of Zr, Hf, or Ce (x = 0.025) into potassium orthophosphate leads to stabilization of highly-conductive -modification of K₃PO₄ at room temperature. Maximum values of potassium-cation conduction in all the systems studied correspond to regions of single-phase solid solutions based on K₃PO₄. The maximum electroconductivity (0.005 S cm^–1 at 300°C, 0.1 S cm^–1 at 700°C) and the smallest activation energies (32–35 kJ mol^–1) take place in the systems with Zr and Hf.     

Determination of trace level impurities in uranium compounds by ICP-AES after organic extraction

The determination was studied of Al, B, Be, Cd, Ca, Co, Cu, Mg, Mn, Mo, Pb, Si, Sn, V, Cr, Ni, and Fe as trace level impurities in uranium compounds by ICP-AES after extraction of uranium with three different mixtures of di-(2-ethyl-hexyl) phosphate (D2EHP) and tri-(2-ethyl-hexyl)-phosphate (T2EHP) in solvents like toluene, carbon tetrachloride, hexane and cyclohexane. The study was carried out in presence of different concentrations of HCl and HNO₃. A single extraction with D2EHP in cyclohexane using nitric acid as matrix was sufficient to reduce the U₃O₈ concentration from 100 g/l to 100 g/ml. The ICP-AES instrumentation applied, allowed the determination of metal concentrations ten-times lower than those usually found in nuclear grade U₃O₈. To check the efficiency of the extraction and the accuracy of the proposed method, Certified Reference Materials were used in the dissolution and extraction steps. The method described can be used for the determination of trace metals in nuclear grade U₃O₈.     

In-situ vaporization and matrix removal for the determination of rare earth impurities in zirconium dioxide by electrothermal vaporization inductively coupled plasma atomic emission spectrometry

A novel method for the determination of trace rare earth impurities in ZrO₂ powder has been developed based on electrothermal vaporization inductively coupled plasma atomic emission spectrometry. A polytetrafluoroethylene slurry was used as a fluorinating reagent to convert both the matrix (Zr) and the analytes (rare earth elements) into fluorides with different volatilities at a high temperature in a graphite furnace. The more volatile ZrF₄ was removed in-situ by selective vaporization prior to the determination of the analytes, removing matrix spectral interferences. Under optimum operating conditions, the absolute detection limits of the analytes varied from 0.04 ng (Yb) to 0.50 ng (Pr) with relative standard deviations less than 5%. The recommended approach has been successfully applied to the determination of trace rare earth impurities (La, Pr, Eu, Gd, Ho and Yb) in ZrO₂ powder and the results were in good agreement with those obtained by pneumatic nebulization inductively coupled plasma atomic emission spectrometry after the separation of the matrix using a solvent extraction procedure.     

Influence of the preparation conditions of Pd‐ZrO2 and AuPd‐ZrO2 nanoparticle–decorated functionalised MWCNTs: Electron spectroscopy study aided with the QUASES

The Pd, AuPd, and ZrO₂ nanoparticle–decorated functionalised multiwalled carbon nanotubes (f‐MWCNTs) were reported as efficient catalysts of formic acid (FA) electro‐oxidation. Different preparation conditions influence their chemical and structural properties analysed by X‐ray photoelectron spectroscopy aided with the quantitative analysis of surfaces by electron spectroscopy. Different reduction procedures such as NaBH₄, a polyol microwave‐assisted method (PMWA), and a high pressure microwave reactor (HPMWR) were applied for decorating ZrO₂/f‐MWCNTs with Pd and AuPd nanoparticles. The ZrO₂ nanoparticles are attached through oxygen groups to the surface of f‐MWCNTs. In NaBH₄ and HPMWR procedures, Pd nanoparticles precipitate predominantly on ZrO₂ of nearly nominal stoichiometry, whereas in PMWA procedure, Pd and AuPd nanoparticles precipitate predominantly on the surface of f‐MWCNTs, bridging with oxygen groups and ZrO_x (x < 2) and leading to Pd‐O‐Zr phase formation. Strong reducing procedures (NaBH₄ and FA) led to smaller Pd nanoparticle size, Pd oxide content, and PdO_x overlayer thickness in contrary to weak reduction procedures (HPMWR and PMWA). The highest content of Pd‐O‐Zr phase appeared for Pd predominant precipitation on ZrO₂ nanoparticles (HPMWR) in contrary to Pd and AuPd predominant precipitation on surface of f‐MWCNTs (NaBH₄ ~ FA > PMWA). Larger content of Pd‐O‐Zr phase in AuPd‐decorated ZrO₂/f‐MWCNTs in contrary to Pd‐decorated sample (PMWA) could be justified by different electronic properties of nanoparticles. The FA treatment of Pd and AuPd‐ZrO₂/f‐MWCNTs samples provided decreasing Pd oxide content, overlayer thickness, nanoparticle size, increasing nanoparticle surface coverage and density, amount of Pd‐O‐Zr, what results from reduction of oxygen groups bridging with Pd and ZrO_x nanoparticles, also through Pd‐O‐Zr phase.     

On-line coupled ion chromatography-ICP-(AES, MS) and electro thermal vaporisation-ICP-MS in use for ultra trace analysis of high purity rhenium

This work presents the benefits of coupling techniques such as Electro Thermal Vaporisation (ETV)-ICP-MS and Ion Chromatography (IC)-ICP-(AES, MS) for ultra trace analysis in a high purity rhenium powder sample. Direct analysis using ICP-AES suffers from poor detection limits and allows trace analysis only above 1 g/g for most analytes. ICP-MS analysis of trace elements is more sensitive, but signal depression caused by the heavy Re-ions limits trace analysis to concentrations of 50–100 ng/g analyte in the solid sample. Coupling Ion Chromatography with ICP-spectrometers, combined with time resolved measurement (IC-ICP-TRM) of the elution signals, was used to enhance the sensitivity of both ICP-AES and ICP-MS. Resulting detection limits are in the very low ng/g to pg/g range. Coupling of ETV and ICP-MS offers the possibility of eliminating the volatile Re₂O₇ matrix by thermal pretreatment and allows ICP-MS measurements without matrix interferences caused by Re. Results from these methods are compared with Glow Discharge Mass Spectrometry (GDMS) analysis, a semiquantitative solid state technique. The results are also compared with the manufacturers' specifications to show the power of modern routine analysis using ICP-AES or FAAS.     

Determination of trace impurities in high-purity zirconium dioxide by inductively coupled plasma atomic emission spectrometry using microwave-assisted digestion and wavelet transform-based correction procedure

This paper describes a rapid, accurate and precise method for the determination of trace Fe, Hf, Mn, Na, Si and Ti in high-purity zirconium dioxide (ZrO₂) powders by inductively coupled plasma atomic emission spectrometry (ICP-AES). The samples were dissolved by a microwave-assisted digestion system. Four different digestion programs with various reagents were tested. It was found that using a mixture of sulfuric acid (H₂SO₄) and ammonium sulfate ((NH₄)₂SO₄), the total sample dissolution time was 30 min, much shorter than that required for conventional digestion in an opening system. The determination of almost all of the target analytes suffered from spectral interferences, since Zr shows a line-rich atomic emission spectrometry. The wavelet transform (WT), a recently developed mathematical technique was applied to the correction of spectral interference, and more accurate and precise results were obtained, compared with traditional off-peak background correction procedure. Experimental work revealed that a high Zr concentration would result in a significant decrease in peak height of the analyte lines, which was corrected by standard addition method. The performance of the developed method was evaluated by using synthetic samples. The recoveries were in the range of 87-112% and relative standard deviation was within 1.1-3.4%. The detection limits (3σ) for Fe, Hf, Mn, Na, Si and Ti were found to be 1.2, 13.3, 1.0, 4.5, 5.8 and 2.0 μg g⁻¹, respectively. The results showed that with the microwave-assisted digestion and the WT correction, the detection limits have improved by a factor of about 5 for Fe, 4 for Mn and Ti, 3 for Si, and 2 for Hf and Na, respectively, in comparison with conventional open-system digestion and off-peak correction. The proposed technique was applied to the analysis of trace elements above-mentioned in three types of ZrO₂ powders.     

Nature and conditions of formation of structural defects in zirconium(IV) oxide in the course of its preparation from zirconium hydroxide

The nature of paramagnetic defects in nanosized ZrO₂ samples prepared by the sol-gel method was studied by ESR. Conditions of formation of different centers (Zr³⁺, F centers, O^?, O ₂ ^? ) in ZrO₂ were elucidated. The Zr³⁺ and O^? centers arise in the course of thermal dehydration of Zr(OH)₄ under the conditions when the formation of a Zr-O-Zr bridging bond is hindered. The F centers are formed in ZrO₂ on heating in a reducing atmosphere or as a result of structural rearrangements accompanied by a decrease in the amount of lattice oxygen in the coordination surrounding of Zr(IV).     

Pt4ZrO2/C cathode catalyst for improved durability in high temperature PEMFC based on H3PO4 doped PBI

In this paper, Pt₄ZrO₂/C was prepared and compared with commercial Pt/C (46.6 wt.% TKK) in terms of the durability as cathode catalyst in a high temperature proton exchange membrane fuel cell (PEMFC) based on H₃PO₄ doped polybenzimidazole (PBI) by a potential sweep test. The catalysts before and after the potential sweep test were characterized by rotating disk electrode (RDE), X-ray diffraction (XRD), transmission electron microscopy (TEM) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). After 3000 cycles potential sweep test, the overall performance loss of the Pt₄ZrO₂/C membrane electrode assembly (MEA) was less than that of the Pt/C MEA. The RDE results demonstrated that the oxygen reduction reaction (ORR) activity of the as-prepared Pt₄ZrO₂/C is nearly the same as TKK-Pt/C. The XRD and TEM results showed that Pt₄ZrO₂/C catalyst presented higher sintering resistance than commercial Pt/C catalyst during the potential sweep test. This may be attributed to the addition of ZrO₂, which acts an anchor to inhibit the adjacent platinum particles to agglomerate. The ICP-AES results of Pt₄ZrO₂/C cathode catalyst before and after the potential sweep test showed that the composition of Pt and Zr were very near the nominal atomic ratio of Pt:Zr, which reflected that Pt₄ZrO₂/C catalyst had a good stability during the potential sweep test. In brief, the preliminary results indicate that Pt₄ZrO₂/C catalyst is a good candidate of Pt/C catalyst in high temperature PEMFC based on H₃PO₄ doped PBI for achieving longer cell life-time and higher cell performance.     

Direct determination of trace elements in niobium,tantalum and their oxides by inductively coupled plasma atomic emission spectrometry after microwave dissolution

Analytical schemes for the determination of trace elements in high-purity niobium, tantalum and their oxides are proposed. The schemes are based on microwave dissolution of the metals and oxides followed by inductively coupled plasma atomic emission spectrometry (ICP-AES) determination of impurities in the solutions. The possibilities of interelement and off-peak background corrections in ICP-AES analysis are discussed. The accuracy of the results obtained is confirmed by the determination of trace elements after a matrix sorption separation procedure. For a number of elements, a comparison of the results obtained by ICP-AES without and with the matrix separation procedure and by electrothermal atomic absorption spectrometry (ETAAS) shows good agreement. The limits of detection for direct ICP-AES determination are in the range 0.4*1.0 μg g⁻¹ for Ba, Ca, Fe, Mg, Mn, Y and La; between 2.0 and 10.0 μ g⁻¹ for B, Cd, Co, Cr, Cu, Hf, Mo, Na, Nb, Ni, Pb, Sr, Ti, Zr and Ta; and for K, Sb and W a detection limit of 20 μ g⁻¹ is achieved. The schemes proposed are intended for rapid routine analysis.     

Thermodynamic investigation of zirconium diselenite

Summary On the basis of calorimetric research of selenium dioxide, zirconium dioxide and zirconium diselenite dissolution reactions in the hydrofluoric acid solution under 298 K a standard enthalpy of Zr(SeO₃)₂ formation reaction from ZrO₂ and SeO₂ and a standard enthalpy of zirconium diselenite formation have been obtained. The value of enthalpy has been equal to -58.1±3.43 kJ mol^-1 in ZrO_2(solid)+2SeO_2(solid) Zr(SeO₃)_2(solid) reaction. The standard enthalpy of zirconium diselenite formation is equal to H_f,298⁰Zr(SeO₃)_2(solid)= -1603.2±3.8 kJ mol^-1. The H_f,298⁰ Zr(SeO₃)_2(solid) value has been determined for the first time.     

Direct multielement determination of trace elements in boron carbide powders by direct current arc atomic emission spectrometry using a CCD spectrometer

The use of direct current arc atomic emission spectrometry (DC-arc-AES) with a CCD spectrometer for the direct determination of the trace impurities Al, Ca, Cr, Cu, Fe, Mg, Mn, Na, Ni, Si, Ti, and Zr in three well characterized boron carbide powders is described. The detection limits obtained by the procedure were found to be between 0.2 (Mg) and 25 (Na) ??g?g^?1 for the above elements. Three boron carbide powder samples with trace element concentrations between 0.9 (Cu) and 934 (Si) ??g?g^?1 for Al, Ca, Cr, Cu, Fe, Mg, Mn, Na, Ni, Si, Ti, and Zr ?? including the standard reference material ERM?-ED102 ?? were analyzed by DC-arc-AES. The relative standard deviations for 9 measurements when using 5.0?±?0.3?mg of the respective samples were found to vary from 6.2 to 27% for Al and Cu, respectively. The trace elements Al, Ca, Cr, Cu, Fe, Mn, Ni, Si, Ti and Zr could be determined in the standard reference material and their concentrations determined by DC-arc AES were found to be between 89 and 116% of the accepted values. Fe and Ti were determined by DC-arc AES in the three boron carbide samples as well as in Al₂O₃, BN, SiC, coal fly ash, graphite and obsidian rock. The correlation coefficients of the plots of the net intensities versus the accepted values over the concentration ranges from 18 to 1750 and from 6 to 8000???g?g^?1 are 0.999 and 0.990 for Fe and Ti, respectively.

Sol-gel ZrO2 coatings for chemical protection of stainless steel

ZrO₂ coatings deposited on 316 L stainless steel sheets were synthesized by sol-gel method using Zr(OC₃H₇)₄ as precursor and isopropanol, glacial acetic acid, and water as solvents for application with ultrasounds. Different solutions for dip-coating were prepared with compositions varying between 0.025 and 0.9 mol/dm³ of ZrO₂. X-ray diffraction shows that the films densified at 800°C are crystalline with a tetragonal structure. The thickness of the coatings varied from 0.35–0.75 m. The influence of the ZrO₂ coatings on the corrosion behavior of stainless steel substrates in aqueous NaCl was studied through potentiodynamic polarization curves at 1 mV/s. The values of the electrochemical parameters allow for an explanation of the role of the films in the increased resistance of steel against corrosion in moderately aggressive environments.     

Analysis of silicon carbide powders with ICP-MS subsequent to sample dissolution without and with matrix removal

ICP-MS has been employed for the analysis of silicon carbide powders in connection with high pressure acid decomposition without and with matrix removal by evaporation. The powder is decomposed by treatment of a 250 mg sample with a mixture of HNO₃, H₂SO₄ and HF. Prior to the analyses with ICP-MS the solutions have to be diluted to a matrix concentration of 500 g/ml related to SiC in order to realize full long-term precision. The results obtained for Li, B, Na, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Ag, Cd, In, Sn, Sb, Ba, La, Ce, Pr, Nd, Hf, Ta, W, Tl, Pb, Bi, Th and U in SiC powder S-933 are shown to be in good agreement with those of independent methods, such as INAA, ICP-AES with slurry atomization and ICP-AES subsequent to sample decomposition. For extending the use of ICP-MS to elements such as Mg, Ca, Sc and Ti at the relevant concentrations in SiC powders, a more effective matrix removal by evaporation of the decomposition solution to near dryness has been successfully applied. Its advantages have been proven by the results of high resolution ICP-MS. It has been found by analyses of the treated sample solutions for the residual Si and C with ICP-MS that over 99% of the matrix and also of the acids used for decomposition are removed. For B, Al and Fe losses were found to occur at concentration levels of some g/g, 200 g/g and 300 g/g, respectively, and all other elements were detected with very good recoveries. For all 36 elements investigated in this work the detection limits could be improved from the ng/g to the pg/g range by removal of the matrix. The analytical range could be improved, in particular for In, Tl, Bi and U.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Determination of impurities in silicon carbide powders

Summary The analysis of SiC powders used for the production of high-performance ceramics was investigated by combined procedures as well as by a direct technique including atomic spectrometric detection. For the combined chemical procedure, SiC powders (0.25 g) were completely dissolved in a mixture of HNO₃, HF and fuming H₂SO₄ in an autoclave at 240°C within 8 to 20 h. In the final 0.5% w/v solution 13 elements were determined by electrothermal atomic absorption spectrometry (ETAAS) and by inductively coupled plasma atomic emission spectrometry (ICP-AES). With acid decomposition the detection limits for Ca, Cd, Cr, Cu, Mg, Mn and Zn were found to be in the range of 0.1–1 g/g; those for Al, B, Fe, Ni, Ti and V are at the 1–5 g/g level. With a Babingtontype nebulizer 1% slurries of SiC can be directly analyzed by ICP-AES. Calibration was performed by standard addition of aqueous solutions of the elements to be determined and the detection limits are close to those of ETAAS subsequent to pressure decomposition. The required analysis time was reduced from approx. 24 h to 30 min. First results for Ca, Cr, Cu, Mg, Mn, Ti and V as well as the needs to overcome systematic errors of this method, e.g. for Fe, are communicated.Part of this paper was presented at XI. International Symposium of Microtechniques, Wiesbaden, FRG, Aug. 28th–Sept. 1st 1989     

New alkaline earth-zirconium oxalates M2Zr(C2O4)4·nH2O (M=Ba, Sr, Ca) synthesis, crystal structure and thermal behavior

Three new alkaline earth-zirconium oxalates M₂Zr(C₂O₄)₄·nH₂O have been synthesized by precipitation methods for M=Ba, Sr, Ca. For each compound the crystal structure was determined from single crystals obtained by controlled diffusion of M²⁺ and Zr⁴⁺ ions through silica gel containing oxalic acid. Ba₂Zr(C₂O₄)₄·7H₂O, monoclinic, space group C2/c, a=9.830(2), b=29.019(6), , , , Z=4, R=0.0427; Sr₂Zr(C₂O₄)₄·11H₂O, tetragonal, space group I4₁/acd, a=16.139(4), , ,Z=8, R=0.0403; Ca₂Zr(C₂O₄)₄·5H₂O, orthorhombic, space group Pna2₁, a=8.4181(5), b=15.8885(8), , , Z=4, R=0.0622. The structures of the three compounds consist of chains of edge-shared MO₆(H₂O)_x (x=2 or 3) polyhedra connected to ZrO₈ polyhedra through oxalate groups. Depending on the arrangement of chains, the ZrO₈ polyhedron geometry (dodecahedron or square antiprism) and the connectivity, two types of three-dimensional frameworks are obtained. For the smallest M²⁺ cations (Sr²⁺, Ca²⁺), large tunnels are obtained, running down the c direction of the unit cell, which can accommodate zeolitic water molecules. For the largest Ba²⁺ cation, the second framework is formed and is closely related to that of Pb₂Zr(C₂O₄)₄·nH₂O. The decomposition at 800°C into strontium carbonate, barium carbonate or calcium oxide and MZrO₃ (M=Sr, Ba, Ca) perovskite is reported from thermal analyses studies and high temperature X-ray powder diffraction.     

Direct analysis of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powders by total reflection X-ray fluorescence spectrometry

A direct analysis procedure for the determination of trace impurities of Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga in Al₂O₃ ceramic powders by total reflection X-ray fluorescence spectrometry (TXRF) is described. The powders were analysed in the form of slurries containing 1–10 mg mL^–1 of powder. The use of the procedure in the case of powders with differing grain size and for different slurry concentrations was investigated. Three different quantification possibilities were compared, namely the use of Al as a matrix component, the use of Fe as a trace element contained in the sample or of Co added in concentrations of 200 g g^–1 as internal standard. The homogeneity of elemental distributions in sample layers deposited on the TXRF quartz carriers by evaporating 5 L of the 10 mg mL^–1 slurries was studied by scanning the 4- to 5-mm-diameter spots of two samples by synchrotron radiation TXRF at Hasylab. For powders with differing graininess but mainly finer than about a few 10 m, no systematic influence of the grain size on the accuracy of the determinations of Ca, V, Fe, Ni, Cu and Zn could be observed. The measurement precision, however, seemed to be limited by inhomogeneous distributions of the trace elements in the samples as testified by the synchrotron radiation TXRF scans. Detection limits of the developed TXRF procedure for Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga were found to be in the 0.3–7 g g^–1 range and were shown to increase slightly with the grain size of the samples. Quantification using Al (matrix) as internal standard led to systematically higher values out of the accuracy required, whereas the other two approaches in all cases led to reliable results.Dedicated to the memory of Wilhelm Fresenius     

Effect of α-Hydroxyketones as Chelate Ligands on Dip-Coating of Zirconia Thin Films

The stabilization effects of -hydroxyketones such as acetoin, acetol, and their imine derivatives of monoethanolamine (MEA) on the 2-propanol solution of metal alkoxides (Al, Ti, Zr, Nb and Ta) were investigated. The hydroxyketones, especially acetoin which has a moderate boiling point around 150°C, were found to have a stabilization effect on the alkoxides of Ti^IV, Nb^V and Ta^V already in their molar ratios of 2, while the Zr^IV alkoxide was stabilized at the molar ratio of 4. By sol-gel processing using this acetoin-stabilized solution, crystallized ZrO₂ thin films could be prepared at temperatures as low as 400°C, which was lower than that from a diethanolamine (DEA)-stabilized precursor (450°C). The films prepared in this study showed a high transparency (more than 90%, UV-VIS spectroscopy), suggesting that the use of chelate ligands with low boiling points is a good way to lower the crystallization temperature of sol-gel-derived ZrO₂ thin films. The Zr complexes of the imines made by the reaction between the hydroxyketones and MEA were stable and photosensitive (<500 nm), making it possible to pattern ZrO₂ films by photo-irradiation of their gel films.     

Crystal Structure of the Ca2+ Supramolecular Complex with Cucurbituryl {[Ca(H2O)3(HSO4)(CH3OH)]2(C36N24O12H36)}(HSO4)2 · 4H2O

The calcium(II) supramolecular complex with cucurbituryl of composition {[Ca(H₂O)₃(HSO₄)(CH₃OH)]₂(C₃₆N₂₄O₁₂H₃₆)}(HSO₄)₂ · 4H₂O is obtained by slow diffusion of methanol into a calcium(II) solution in 2 M H₂SO₄; its crystal structure is determined by X-ray diffraction analysis. The crystals are triclinic, a = 10.4030(9) Å, b = 11.936(1) Å, c = 15.119(1) Å, = 69.829(6)°, = 72.019(5)°, = 70.171(7)°, V = 1618.1(2) ų, space group P , Z = 1, _calcd = 1.754 g/cm³. The crystal structure is a pseudohexagonal packing of {[Ca(H₂O)₃(HSO₄)(CH₃OH)]₂(C₃₆N₂₄O₁₂H₃₆)}²⁺ cylinders shifted by half translation along the a axis. The cylinders are linked via hydrogen bonds, with the crystallization water molecules and HSO^– ₄ anions arranged in the channels.     

Metal–organic framework derived Pd/ZrO2@CN as a stable catalyst for the catalytic hydrogenation of 2,3,5‐trimethylbenzoquinone

Metal–organic frameworks (MOFs) have recently been identified as versatile sacrificing templates to construct functional nanomaterials for heterogeneous catalysis. Herein, we report a thermal transformation strategy to directly fabricate metal Pd nanoclusters inlaid within a ZrO₂@nitrogen‐doped porous carbon (Pd/ZrO₂@CN) composite using Pd@NH₂‐UiO‐66(Zr) as a precursor that was pre‐synthesized by a one‐pot hydrothermal method. The developed Pd/ZrO₂@CN as a robust catalyst delivered remarkable stability and activity to the catalytic hydrogenation of 2,3,5‐trimethylbenzoquinone (TMBQ) to 2,3,5‐trimethylhydroquinone (TMHQ), a key reaction involved in vitamin E production. The hydrogenation was carried out at 110 °C with 1.0 MPa H₂, and it resulted in 98% TMHQ yield as the sole product over five consecutive cycles, outperforming the analogue Pd/ZrO₂@C without nitrogen doping templated from Pd@UiO‐66(Zr). The excellent catalytic properties of Pd/ZrO₂@CN likely originated from the highly stable ultrafine Pd nanoclusters inlaid within ZrO₂@CN matrix on account of the strong interaction between N and Pd, as well as on the Lewis acidity of ZrO₂, which was beneficial to the hydrogenation.