Wallace O’Neil Parker

Proton exchange and isomerisation reactions of photochromic and reverse photochromic spiro-pyrans and their merocyanine forms

Photochromic 1′,3′,3′-trimethyl-6,8-dinitro-spiro- [2H-1-benzopyran-2,2-indoline], (6,8-dinitro BIPS) has been studied in different solvents using 1H-NMR techniques, UV/visible spectroscopy, X-ray diffraction and electrospray ionisation mass spectroscopy (ESI-MS). Molar decadic absorption coefficients for 6,8-dinitro BIPS were found to range between 35000–45000 d mol-1 cm-1. 1H–1H NOESY and 1H-NMR experiments have established that in solution the merocyanine form of 6,8-dinitro BIPS is in rapid exchange between the trans-trans-cis (TTC) and trans-trans-trans (TTT) isomers. The 3B proton on the central bridging double bond of spiro-pyran merocyanines is labile in organic solvents. The closed form of 6,8-dinitro BIPS enantiomerises about the spiro C(2) carbon at a rate of 18 s-1 at 300 K. The activation energy for this process was estimated to be 46 kJ mol-1 using dynamic NMR.

Metal Substitution in Keggin-Type Tridecameric Aluminum-Oxo-Hydroxy Clusters

The species resulting from a typical preparation for metal-substituted hybrids of the Keggin tridecamer, Al13 or [AlO4Al12(OH)24(OH2)12]7+, were examined by performing 27Al NMR on the solutions during aging and by studying the precipitated sulfate salts via solid state 27Al NMR and powder X-ray diffraction (XRD). Aqueous mixtures (0.25 mol L-1) of AlCl3 and another metal ion (M), in a 12:1 mole ratio (Al:M), where M = Fe3+, Zn2+, Ga3+, In3+, Sn2+, La3+, and Bi3+, were subjected to forced hydrolysis by addition of NaOH (1.0 mol L-1) until OH/(Al + M) = 2.25, and the kinetics of Al13 formation and disappearance with aging at 80 °C was monitored by 27Al NMR spectroscopy. Al13 units polymerize on aging with an apparent rate constant (k) of 4.8(8) × 10-2 h-1 to form a species referred to as AlP2. Only the solutions containing Ga3+ and Sn2+ exhibited faster Al13 conversion rates. GaAl12 forms quickly at 80 °C (k = 0.54 h-1) and is more stable than AlP2. Sn2+ apparently promotes AlP2 formation (k = 0.38 h-1). XRD and solid state NMR reveal that only the Ga hybrid can be prepared by this method. No hybrid formation was evidenced using M = Mg2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, In3+, La3+, or Ce3+ at 25 °C or M = Co2+ or La3+ under reflux conditions. Isostructural (cubic symmetry) single crystals were obtained for the sulfate salts of Al13 and GaAl12. Single-crystal XRD analysis of these two polyoxocations provides the first rigorous comparison between them and shows they have very similar structures. The main crystallographic data for Al13 and GaAl12 are as follows:  Na[AlO4Al12(OH)24(H2O)12](SO4)4·10H2O, cubic, F4̄3m, a = 17.856(2) Å, Z = 4; Na[GaO4Al12(OH)24(H2O)12](SO4)4·10H2O, cubic, F4̄3m, a = 17.869(3) Å, Z = 4. Thus, the greater thermal stability of GaAl12 cannot be rationalized in terms of the overall geometric considerations, as suggested by others. Solid state NMR also shows the coordination symmetries of the outer 12 Al nuclei in both clusters to be similar.

Hierarchical hybrid organic-inorganic materials with tunable textural properties obtained using zeolitic-layered precursor.

Novel layered zeolitic organic-inorganic materials have been synthesized using a two-dimensional zeolite precursor IPC-1P prepared by a top-down approach from zeolite UTL. The formation of porous materials containing organic linkers or polyhedral oligomeric siloxane covalently bonded to zeolite layers in the interlayer space was confirmed by a variety of characterization techniques (N2/Ar sorption analysis, XRD, (29)Si and (13)C NMR, TEM). The organic-inorganic porous hybrids obtained by intercalation with silsesquioxane posessed layered morphology and contained large crystalline domains. The hybrids exhibited mesoporous or hierarchical micro-/mesoporous systems, stable up to 350 °C. Textural properties of the formed zeolitic organic-inorganic materials can be controlled by varying the linker or synthetic conditions over a broad range. Surface areas and pore volumes of synthesized hybrids significantly exceed those for parent zeolite UTL and corresponding swollen material; the amount of micropores increased with increasing rigidity and size of the organic linker in the order biphenyl > phenylene > ethanediyl.

Spectroscopic studies of LaHY-FAU catalyst deactivation in the alkylation of isobutane with 1-butene

Abstract The carbonaceous deposits formed on LaHY-FAU used in a semi-batch reactor at 353 K to alkylate isobutane with 1-butene have been examined by in situ UV-VIS, FT-IR, and 13C CP/MAS NMR spectroscopies. Only UV-VIS studies evidence unsaturated carbenium ions immediately on adsorption of 1-butene and or 1-butene/isobutane mixture. These ions are part of high molecular weight oligomers (low-temperature carbonaceous deposits) which remain attached to the active site, effecting catalyst deactivation by poisoning. Unsaturated carbenium ion formation is favored by higher reaction temperature (up to 523 K), longer contact times (lower LSHV) and increased Lewis acidity. The presence of isobutane greatly reduces oligomer formation. Thermal treatment of the used catalyst under vacuum causes the low-temperature deposits to desorb from the active site and conversion to aromatics (which remain up to 823 K). The acidic OH groups of the active sites are to a large part regenerated by this treatment yet the initial catalytic activity cannot be fully restored.

Structural characterization of as-synthesized B- and Ti-containing MFI-type molecular sieves☆

The influence of tetrapropylammonium ( TPA) ions on the structural properties of as-synthesized Ti- (TS-1) and B-containing (BOR-C ) MFI zeolites crystallized from alkali-free gels is investigated. Thermogravimetric analysis shows that the negative charge of the BOR-C framework is compensated by the TPA ions, while only ‘soft’ interactions between TPA and Ti sites are observed. Rietveld analysis of the synchrotron X-ray powder diVraction patterns reveals that incorporation of Ti and B causes an expansion and a contraction of the MFI framework, respectively. Regression curves describing the unit cell parameters variation can be used to determine the real framework composition. The presence of TPA ions inside the pores strongly influences the apparent d TiMO and d BMO tetrahedral bond distances, which are shorter than those in the calcined forms. The mobility of the TPA cations in silicalite-1, TS-1 and BOR-C samples with the highest Ti and B content is studied by 13C NMR and molecular dynamics simulations. As expected, the TPA cation mobility increases as the pore size increases (BOR-C

Heteropolyacids as effective catalysts to obtain zero sulfur diesel

This paper deals with the catalytic properties of different supported heteropolyacids (HPAs), both molybdenum- and tungsten-based, in the oxidative desulfurization process of diesel. We are jointly developing a new oxidative desulfurization process, aimed at reducing the sulfur content in diesel to less than 10 ppm (parts per million) using in situ produced peroxides. In this new process, high-molecular-weight organosulfur compounds, such as 4,6-dimethyl-dibenzothiophene (DMDBT), difficult to be eliminated by conventional hydrodesulfurization, are oxidized to the corresponding sulfones and subsequently removed by adsorption. Molybdenum-based HPAs, with Keggin structure, proved to be the most active and selective catalysts for oxidizing DMDBT with on-stream lifetimes exceeding 1500 h time on stream (t.o.s.).

Synthesis and characterization of borosilicates with the EUO framework topology

Abstract B-EUO, a borosilicate with the EUO framework topology was successfully synthesized by using N,N,N,N′,N′,N′-hexamethyl-1,6-hexanediammonium (hexamethonium) as a structure-directing agent. The effective incorporation of B in the EUO framework was confirmed by 11 B MAS NMR, TG and XRD analyses. Up to ∼8 B atoms/unit cell were incorporated in the EUO framework, which corresponds to the number of ammonium groups accommodated in the pores. EUO was obtained also in the ternary B–Al–Si system, with the Al quantitatively incorporated into the framework. A structural model was derived for the as-synthesized EUO sample, with the position of the hexamethonium ion determined with the Quench Dynamics protocol, a procedure that combines high-temperature molecular dynamics and energy minimization techniques. The model was successfully employed for refining the experimental XRD profiles by the Rietveld method.

Interaction of phosphorus trichloride with zeolites

The paper presents a detailed 27Al, 29Si, and 31P n.m.r. and i.r. study of the interaction of zeolites with PCl3. The faujasite framework collapses upon the PCl3 treatment, whereas the mordenite framework is more stable. Phosphorus can be incorporated into zeolites as surface phosphite or phosphate groups but cannot be introduced in a tetrahedral framework position. HM-MOR was dealuminated with PCl3 in one step, whereas the HY-FAU was first dealuminated with SiCl4 followed by a COCl2 treatment, and finally dealumination was completed with PCl3. The HM-MOR sample is only partially dealuminated, as confirmed by 29Si and 27Al n.m.r. data. The dealumination of HY-FAU zeolite is quasi-complete, although a high amount of amorphous aluminosilicate is also formed during the dealumination steps. 31P n.m.r. data show the presence of dihydrogenophosphate SiOP=O(OH)2 and phosphite (SiO)2P=O(H) groups attached to the surface of both zeolites. Infrared data reveal the presence of the phosphite group. Part of the phosphorus is found in a crystalline aluminophosphate phase in the HM-MOR sample, but the aluminophosphate phase of the Y zeolite sample proved to be amorphous with the P/AI molar ratio much lower than unity.

Stability upon thermal treatment of coked zeolite beta

Abstract Dealumination during thermal treatment of zeolite Beta was examined. Repeated thermal treatments of zeolite impregnated with poly-alkylated tars (coked Beta) were made to simulate prolonged industrial usage. The partial structural collapse caused by each impregnation/calcination was quantified by XRD and the migration of aluminum (from framework to extra-framework sites) was evidenced by 27 Al MAS NMR and IR spectroscopies. Non-impregnated Beta was thermally stable up to 750°C. On the contrary, limited but significant framework dealumination occurred during thermal treatment of impregnated zeolite Beta, due to H 2 O produced by the combustion of the organic species trapped inside the pores. These results allowed the design of an appropriate regeneration procedure for the proprietary zeolite Beta-based catalyst, which is necessary to avoid removal of framework aluminum and zeolite structure collapse.

Influence of zeolite pore structure on benzene propylation to iso-/n-propylbenzene

The isomerization of cumene (isopropylbenzene, i-PB) to n-propylbenzene (n-PB), considered to proceed via a 1,2-diphenylpropane intermediate (1), was studied by theoretical and experimental methods to investigate the importance of shape selectivity effects for different zeolites. The location and energetics of 1, and also of the intermediate 2,2-diphenylpropane (2) involved in transalkylation of i-PB, were determined by molecular mechanics and dynamics calculations to evaluate the influence of the pore architecture on the two reactions. Only zeolites with ID linear channel systems (e.g. MTT, MTW) were predicted to preferentially stabilize intermediate 1 with respect to 2, while limited differences were observed for 3D interconnected porous systems (e.g. *BEA, MOR, MFI, FAU). Preliminary in-situ 13C NMR studies (without MAS) of benzene and cumene (3:1) adsorbed on H+ form zeolites found n-PB production (at 473 K) to increase as: Beta < ZSM-5 (MFI) < USY (FAU)≈ ERB-1 (MWW) < MOR.