Lewis Acidic Aluminosilicates: Synthesis, 27Al MQ/MAS NMR, and DFT-Calculated 27Al NMR Parameters.

Porous aluminosilicates are functional materials of paramount importance as Lewis acid catalysts in the synthetic industry, yet the participating aluminum species remain poorly studied. Herein, a series of model aluminosilicate networks containing [L-AlO3] (L = THF, Et3N, pyridine, triethylphosphine oxide (TEPO)) and [AlO4]- centers were prepared through nonhydrolytic sol-gel condensation reactions of the spherosilicate building block (Me3Sn)8Si8O20 with L-AlX3 (X = Cl, Me, Et) and [Me4N] [AlCl4] compounds in THF or toluene. The substoichiometric dosage of the Al precursors ensured complete condensation and uniform incorporation, with the bulky spherosilicate forcing a separation between neighboring aluminum centers. The materials were characterized by 1H, 13C, 27Al, 29Si, and 31P MAS NMR and FTIR spectroscopies, ICP-OES, gravimetry, and N2 adsorption porosimetry. The resulting aluminum centers were resolved by 27Al TQ/MAS NMR techniques and assigned based on their spectroscopic parameters obtained by peak fitting (δiso, CQ, η) and their correspondence to the values calculated on model structures by DFT methods. A clear correlation between the decrease in the symmetry of the Al centers and the increase of the observed CQ was established with values spanning from 4.4 MHz for distorted [AlO4]- to 15.1 MHz for [THF-AlO3]. Products containing exclusively [TEPO-AlO3] or [AlO4]- centers could be obtained (single-site materials). For L = THF, Et3N, and pyridine, the [AlO4]- centers were formed together with the expected [L-AlO3] species, and a viable mechanism for the unexpected emergence of [AlO4]- was proposed.

Copper Phosphinate Complexes as Molecular Precursors for Ethanol Dehydrogenation Catalysts.

Nowadays, the production of acetaldehyde heavily relies on the petroleum industry. Developing new catalysts for the ethanol dehydrogenation process that could sustainably substitute current acetaldehyde production methods is highly desired. Among the ethanol dehydrogenation catalysts, copper-based materials have been intensively studied. Unfortunately, the Cu-based catalysts suffer from sintering and coking, which lead to rapid deactivation with time-on-stream. Phosphorus doping has been demonstrated to diminish coking in methanol dehydrogenation, fluid catalytic cracking, and ethanol-to-olefin reactions. This work reports a pioneering application of the well-characterized copper phosphinate complexes as molecular precursors for copper-based ethanol dehydrogenation catalysts enriched with phosphate groups (Cu-phosphate/SiO2). Three new catalysts (CuP-1, CuP-2, and CuP-3), prepared by the deposition of complexes {Cu(SAAP)}n (1), [Cu6(BSAAP)6] (2), and [Cu3(NAAP)3] (3) on the surface of commercial SiO2, calcination at 500 °C, and reduction in the stream of the forming gas 5% H2/N2 at 400 °C, exhibited unusual properties. First, the catalysts showed a rapid increase in catalytic activity. After reaching the maximum conversion, the catalyst started to deactivate. The unusual behavior could be explained by the presence of the phosphate phase, which made Cu2+ reduction more difficult. The phosphorus content gradually decreased during time-on-stream, copper was reduced, and the activity increased. The deactivation of the catalyst could be related to the copper diffusion processes. The most active CuP-1 catalyst reaches a maximum of 73% ethanol conversion and over 98% acetaldehyde selectivity at 325 °C and WHSV = 2.37 h-1.

Ethanol Dehydrogenation over Copper-Silica Catalysts: From Sub-Nanometer Clusters to 15 nm Large Particles.

Non-oxidative ethanol dehydrogenation is a renewable source of acetaldehyde and hydrogen. The reaction is often catalyzed by supported copper catalysts with high selectivity. The activity and long-term stability depend on many factors, including particle size, choice of support, doping, etc. Herein, we present four different synthetic pathways to prepare Cu/SiO2 catalysts (∼2.5 wt % Cu) with varying copper distribution: hydrolytic sol-gel (sub-nanometer clusters), dry impregnation (A̅ = 3.4 nm; σ = 0.9 nm and particles up to 32 nm), strong electrostatic adsorption (A̅ = 3.1 nm; σ = 0.6 nm), and solvothermal hot injection followed by Cu particle deposition (A̅ = 4.0 nm; σ = 0.8 nm). All materials were characterized by ICP-OES, XPS, N2 physisorption, STEM-EDS, XRD, RFC N2O, and H2-TPR and tested in ethanol dehydrogenation from 185 to 325 °C. The sample prepared by hydrolytic sol-gel exhibited high Cu dispersion and, accordingly, the highest catalytic activity. Its acetaldehyde productivity (2.79 g g-1 h-1 at 255 °C) outperforms most of the Cu-based catalysts reported in the literature, but it lacks stability and tends to deactivate over time. On the other hand, the sample prepared by simple and cost-effective dry impregnation, despite having Cu particles of various sizes, was still highly active (2.42 g g-1 h-1 acetaldehyde at 255 °C). Importantly, it was the most stable sample out of the studied materials. The characterization of the spent catalyst confirmed its exceptional properties: it showed the lowest extent of both coking and particle sintering.

Utilization of Pharmaceutical Technology Methods for the Development of Innovative Porous Metasilicate Pellets with a Very High Specific Surface Area for Chemical Warfare Agents Detection.

Pharmaceutical technology offers various dosage forms that can be applied interdisciplinary. One of them are spherical pellets which could be utilized as a carrier in emerging second-generation detection tubes. This detection system requires carriers with high specific surface area (SSA), which should allow better adsorption of toxic substances and detection reagents. In this study, a magnesium aluminometasilicate with high SSA was utilized along with various concentrations of volatile substances (menthol, camphor and ammonium bicarbonate) to increase further the carrier SSA after their sublimation. The samples were evaluated in terms of physicochemical parameters, their morphology was assessed by scanning electron microscopy, and the Brunauer-Emmett-Teller (BET) method was utilized to measure SSA. The samples were then impregnated with a detection reagent o-phenylenediamine-pyronine and tested with diphosgene. Only samples prepared using menthol or camphor were found to show red fluorescence under the UV light in addition to the eye-visible red-violet color. This allowed the detection of diphosgene/phosgene at a concentration of only 0.1 mg/m3 in the air for samples M20.0 and C20.0 with their SSA higher than 115 m2/g, thus exceeding the sensitivity of the first-generation DT-12 detection tube.

Determination of Zinc, Cadmium, Lead, Copper and Silver Using a Carbon Paste Electrode and a Screen Printed Electrode Modified with Chromium(III) Oxide.

In this study, the preparation and electrochemical application of a chromium(III) oxide modified carbon paste electrode (Cr-CPE) and a screen printed electrode (SPE), made from the same material and optimized for the simple, cheap and sensitive simultaneous determination of zinc, cadmium, lead, copper and the detection of silver ions, is described. The limits of detection and quantification were 25 and 80 µg·L-1 for Zn(II), 3 and 10 µg·L-1 for Cd(II), 3 and 10 µg·L-1 for Pb(II), 3 and 10 µg·L-1 for Cu(II), and 3 and 10 µg·L-1 for Ag(I), respectively. Furthermore, this promising modification was transferred to the screen-printed electrode. The limits of detection for the simultaneous determination of zinc, cadmium, copper and lead on the screen printed electrodes were found to be 350 µg·L-1 for Zn(II), 25 µg·L-1 for Cd(II), 3 µg·L-1 for Pb(II) and 3 µg·L-1 for Cu(II). Practical usability for the simultaneous detection of these heavy metal ions by the Cr-CPE was also demonstrated in the analyses of wastewaters.

Sonochemical precipitation of amorphous uranium phosphates from trialkyl phosphate solutions and their thermal conversion to UP2O7.

Insoluble amorphous precipitates containing uranyl and phosphate ions are obtained by sonication of solutions of three uranyl precursors, UO2(X)2, X=NO3, CH3COO, CH3C(O)CHC(O)CH3 (acetylacetonate, acac), in triesters of phosphoric acid, OP(OR)3, R=Me (trimethyl phosphate, TMP), Et (triethyl phosphate, TEP). TMP and TEP are used as high-boiling solvents and they serve also as a source of phosphate anions. Sonolysis experiments were carried out under flow of Ar at 40°C on a Sonics and Materials VXC 500W system (f=20 kHz, Pac=0.49 W cm(-3)). Powder X-ray diffraction (PXRD) reveals amorphous character of all obtained precipitates. The presence of uranyl and phosphate is evidenced by IR spectroscopy and ICP-OES analysis reveals the content of both U (38.6-43.4 wt%) and P (11.0-13.6 wt%). The thermal behavior of the substances was studied by TG/DSC analysis, which shows weight losses in the range of 19.21-24.08%. On heating the amorphous precipitates to 1000°C, crystalline uranium diphosphate UP2O7 is obtained in all cases as the only crystalline phase. Uranyl(VI) is reduced during thermolysis to U(IV) as there is no characteristic vibration of UO2(2+) in the IR spectra of solid UP2O7 products. The ICP-OES analysis of U and P content in precipitates allowed us to calculate the efficiency of precipitation of uranium from mother liquor and to compare it with the efficiency calculated from the data received by the PXRD and TG/DSC analyses. The efficiency of the uranium removal attained by our sonoprecipitation procedure was typically 30-35%. These sonochemical precipitation reactions providing insoluble uranium phosphates may be potentially interesting models for the description of behavior of uranium-containing waste or reprocessing streams.

Construction of larger molecular aluminophosphate cages from the cyclic four-ring building unit.

New molecular aluminophosphates of different nuclearity are synthesized by a stepwise process and structurally characterized. The alkane elimination reaction of bis(trimethylsiloxy)phosphoric acid, OP(OH)(OSiMe3)2, with trialkylalanes, AlR3 (R = Me, Et, (i)Bu), provides the cyclic dimeric aluminophosphates, [(AlR2{µ2-O2P(OSiMe3)2})2] (R = Me (1), Et (2), (i)Bu (3)). Unsymmetrically substituted cyclic aluminophosphonate [(AlMe2{µ2-O2P(OSiMe3)((c)Hex)})2] (cis/trans-4) is prepared by dealkylsilylation reaction of (c)HexP(O)(OSiMe3)2 with AlMe3. Molecules 1-4 containing the [Al2(µ2-O2P)2] inorganic core are structural and spectroscopic models for the single four-ring (S4R) secondary building units (SBU) of zeolite frameworks. Compound 1 serves as a starting point in construction of larger molecular units by reactions with OP(OH)(OSiMe3)2 as a cage-extending reagent and with diketones, such as Hhfacac (1,1,1,5,5,5-hexafluoropentan-2,4-dione) and Hacac (pentan-2,4-dione), as capping reagents. Reaction of 1 with 4 equiv of Hhfacac leads to new cyclic aluminophosphate [(Al(hfacac)2{µ2-O2P(OSiMe3)2})2] (5), existing in two isomeric (D2 and C2h) forms. Reaction of 1 with 2 equiv of OP(OH)(OSiMe3)2 and 1 equiv of Hhfacac provides a molecular aluminophosphate [AlMe{Al(hfacac)}2{µ3-O3P(OSiMe3)}2{µ2-O2P(OSiMe3)2}2{OP(OSiMe3)3}] (6), while by adding first the Hhfacac and using 3 equiv of OP(OH)(OSiMe3)2 we isolate [Al{Al(hfacac)}2{µ3-O3P(OSiMe3)}2{µ2-O2P(OSiMe3)2}2H{OP(O)(OSiMe3)2}2] (7). These molecules contain units in their cores that imitate 4=1 SBU of zeolite frameworks. Reaction with the order of component mixing 1, Hhfacac, OP(OH)(OSiMe3)2 at a 1:2:2 molar ratio lead to formation of a larger cluster [(Al(AlMe){Al(hfacac)}{µ3-O3P(OSiMe3)}2{µ2-O2P(OSiMe3)2}3)2] (8) containing both S4R and 4=1 structural units. Similarly, Hacac (pentan-2,4-dione) provides an isostructural [(Al(AlMe){Al(acac)}{µ3-O3P(OSiMe3)}2{µ2-O2P(OSiMe3)2}3)2] (9). Both molecules display Al centers in three different coordination environments.

A structurally diverse series of aluminum chloride alkoxides [Cl(x)Al(mu-OR)(y)](n) (R = (n)Bu, (c)Hex, Ph, 2,4-(t)Bu2C6H3).

A diverse series of aluminum chloride alkoxides, [Cl(x)Al(mu-OR)(y)](n) (R = (n)Bu, (c)Hex, Ph, 2,4-(t)Bu(2)C(6)H(3)), was synthesized using the reactions of dichlorethylalane (EtAlCl(2)) with cyclohexanol ((c)HexOH), n-butanol ((n)BuOH), and phenols (PhOH and 2,4-(t)Bu(2)C(6)H(3)OH). Eight molecular products were isolated and structurally characterized. The dimeric [Cl(2)Al(mu-O(c)Hex)(2)AlCl(2)] (1) was the smallest oligomer isolated among the cyclohexanolate derivatives. The adduct of 1 with cyclohexanol is a dinuclear molecule [Cl(2)(HO(c)Hex)Al(mu-O(c)Hex)(2)AlCl(2)] (2) which represents a possible intermediate in the conversion reaction leading to the formation of a trinuclear bicyclic [ClAl{(mu-O(c)Hex)(2)AlCl(2)}(2)] (3). Two polymorphic forms of 3 were isolated. Further coordination of cyclohexanol to the Lewis acidic five-coordinate aluminum atom in 3 provided [Cl(HO(c)Hex)Al{(mu-O(c)Hex)(2)AlCl(2)}(2)] (4) with octahedrally coordinated central aluminum. Compound 4 could be regarded as a precursor to the well-known Mitsubishi (tridiamond) tetranuclear species. The reactions of EtAlCl(2) with less sterically demanding (n)BuOH yielded a cyclic trimer, [Cl(2)Al(mu-O(n)Bu)](3) (5), and a unique trinuclear ionic species, [Cl(2)Al{(mu-OH)(mu-O(n)Bu)AlCl(HO(n)Bu)(3)}(2)]Cl (6) with a linear Al(mu-O)(2)Al(mu-O)(2)Al core. In the reactions with phenols, the aromatic groups preferentially stabilized dimeric structures of [Cl(2)Al(mu-OR)(2)AlCl(2)] (R = Ph, 7; 2,4-(t)Bu(2)C(6)H(3), 8). Since these compounds could be considered as intermediates in the nonhydrolytic condensation reactions of metal halides with metal alkoxides, a mixture of EtAlCl(2) with (c)HexOH was used as a precursor for the nonaqueous synthesis of alumina by alkylhalide elimination.

Sonochemical synthesis of amorphous nanoscopic iron(III) oxide from Fe(acac)3.

Amorphous nanoscopic iron(III) oxide with interesting magnetic properties was prepared by sonolysis of Fe(acac)(3) under Ar in tetraglyme with a small amount of added water. The organics content and the surface area of the Fe(2)O(3) nanoparticles can be controlled with an amount of water in the reaction mixture and it increases from 48 m(2)g(-1) for dry solvent up to 260 m(2)g(-1) when wet Ar is employed. For further monitoring of the particle size and morphology and for the study of the surface, magnetic and thermal properties, the sample with 2 vol.% of H(2)O was chosen. SEM showed nanoscopic composite particles of a uniform size distribution and nearly spherical shapes with an estimated diameter of 20 nm. Such composites are built from amorphous iron(III) oxide nanoparticles (3 nm) embedded in an acetate matrix as proved by TEM and IR spectroscopy. Temperature-dependent Mössbauer spectra demonstrate a very narrow magnetic transition with an unusually low transition temperature around 25K reflecting the system of magnetically non-interacting ultrasmall particles with a narrow size distribution. The in-field (5T) Mössbauer spectrum recorded at 5K shows a minimum change compared to the zero-field spectrum indicating an absence of the long-range magnetic ordering. The composite particles are thermally stable up to 150 degrees C, which is confirmed by DSC, TG, and by the constant surface area. At higher temperatures, acetate groups are removed from the particle surface, which is documented by the increased surface area and disappearance of their IR bands.