Mark E. Davis

Base catalysis by alkali-modified zeolites: I. Catalytic activity

Abstract Isopropanol is reacted over alkali-exchanged X and Y zeolites in the presence and absence of occluded exchange salts at 350 °C and atmospheric pressure. The decomposition of cesium acetate occluded in CsNaY results in the generation of a very active base site. This site improves the acetone activity of the parent CsNaY by an order of magnitude. The CsNaX zeolite, however, does not contain this site after decomposition of the occluded cesium acetate and as a result shows an acetone activity comparable to that observed for the parent CsNaY. For the cesium acetate occluded CsNaY zeolite, the selectivity to acetone is above 97%, and on a surface area basis, the acetone activity is comparable to that found for MgO.

VPI-5: The first molecular sieve with pores larger than 10 Ångstroms

The adsorption properties of a novel family of aluminophosphate based molecular sieves denoted as VPI-5 are described. These molecular sieves are the first to contain pores larger than 10 A. The large pores of the VPI-5 sieves consist of channels circumscribed by eighteen membered rings and possess free diameters of approximately 12–13 A. The VPI-sieves are capable of adsorbing molecules excluded from other molecular sieves.

Supported aqueous-phase catalysts

Abstract This work describes a novel family of catalysts denoted supported aqueous-phase catalysts. These catalysts consist of a water-soluble organometallic complex supported in a thin film of water residing on a high-surface-area hydrophilic solid. The catalytic reaction takes place at the water-organic interface where the organic phase contains the reactants and products. Supported aqueous-phase catalysis is demonstrated by liquid-phase hydroformylation. The solid support used here was either CPG-240 or CPG-350; both are porous glasses with narrow pore volume distributions. The catalytic species, HRh(CO)[ m -P(PhS0 3 Na) 3 ] 3 was synthesized from Rh(CO) 2 (acac) by a new synthetic route and impregnated onto CPG-240. Solution and solid-state 31 P NMR data are consistent with a mobile rhodium species in the aqueous phase in hydrated forms of the catalyst. The hydroformylation of oleyl alcohol (OLOH) was accomplished at 100°C and 5.1 MPa of H 2 /CO (1/1) using 0.002 g Rh/g OLOH. For example, conversions of up to 96.6% could be achieved in 5.5 h. It is postulated that no significant leaching of Rh occurs, since after filtration to remove the solid catalyst the remaining solution showed no activity for either the hydroformylation of additional OLOH or the hydrogenation of added 1-hexene. The observations that (1) OLOH and its hydroformylation products are not water soluble, (2) the double bond of OLOH is internal, and (3) the Rh does not leach into the organic phase demonstrate the concept of SAP catalysis; the immobilized homogeneous catalyst is active at the interface of two immiscible phases.

Base catalysis by alkali modified zeolites: III. Alkylation with methanol

Abstract Ion exchanged CsNaX and CsNaY, cesium acetate impregnated CsNaX ( CsAce CsNaX ) and CsNaY ( CsAce CsNaY ), and MgO have been reacted with isopropanol at 425 °C and atmospheric pressure to assess their acid/base properties at a temperature consistent with that used in the side chain alkylation of toluene with methanol. The results suggest that the ability of the catalysts tested here to promote a base mediated reaction follow the order of MgO > CsAce CsNaY > CsAce CsNaX ⋍ CsNaY > CsNaX . Selectivities to acetone measured at 4.73% conversion follow this order as well, ranging from 95.7% and 93.9% for MgO and CsAce CsNaY , respectively, to 17.6% for the CsNaX. Thus, these catalysts can be grouped into two categories: (i) catalysts which vary in acid/base properties yet possess identical topology (e.g., the zeolites) and (ii) catalysts which vary in topology yet have similar acid/base properties (e.g., MgO and CsAce CsNaY ). These catalysts were compared using the side chain alkylation of toluene, ethane, methane, and acetone with methanol. For the impregnated zeolites, similar toluene conversions were observed. Unlike the impregnated X zeolite, no formaldehyde (i.e., the alkylating agent) was observed in the product stream of the impregnated Y zeolite. Both MgO and CsAce CsNaY had similar methanol decomposition products; i.e., no formaldehyde and high CO formation, yet unlike CsAce CsNaY no toluene conversion was observed for MgO. No conversion of ethane or methane was observed for either impregnated zeolite at 425 °C. Attempts at higher temperatures (e.g., 465 °C) failed also. Acetone was alkylated to methyvinylketone and methylethylketone; however, the majority of the reacted acetone formed products which appear to result from acetone aldol condensations.

Aromatization of n-hexane by platinum-containing molecular sieves II. n-Hexane reactivity

Pt/KL, Pt/BaKL, Pt/KBaKL, Pt/NaY, Pt/CsNaY, Pt/NaFAU(C), Pt/hex, Pt/SSZ-24, Pt/silica, and Pt/carbon were tested as catalysts for the aromatization of n-hexane at 460–510°C and atmospheric total pressure in order to study the influence of Pt cluster size and support acidity/basicity, microstructure, and chemical composition on activity and selectivity. Analysis of the catalytic and NH3 temperature-programmed desorption results from Pt/KL, Pt/BaKL, and Pt/KBaKL reveals that the presence of any acidity increases hydrogenolysis at the expense of benzene production. In addition, no increase in aromatization selectivity is observed by the addition of base sites to a Pt/zeolite catalyst, confirming that aromatization of n-hexane over Pt clusters on nonacidic carriers is monofunctional. High selectivity to benzene over most of the zeolite samples demonstrates that support microstructure does not contribute directly to the aromatization selectivity over Pt catalysts. High selectivity to benzene is observed for a Pt/carbon catalyst suggesting that a zeolitic support is not necessary for good performance. In fact, similar reactivity is obtained from microporous (Pt/SSZ-24) and nonmicroporous (Pt/silica) silica supported platinum catalysts with similar H/Pt values. A clear trend of increasing benzene selectivity with decreasing Pt cluster size is found. These observations suggest that the exceptional reactivity of Pt/KL for the aromatization of n-hexane results from the lack of any acidity in the support and the ability of zeolite L to stabilize the formation of extremely small Pt clusters.

Novel chiral water soluble phosphines II. Applications in catalytic asymmetric hydrogenation

Abstract The results of the homogeneous asymmetric hydrogenation of several dehydroamino acids by rhodium-diene complexes of the chiral ligands; 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(-bis(-p-N,N-dimethylaminophenyl)phosphino)butane, 2a ; 2,4-bis(-bis(-p-N,N-dimethylaminophenyl)phosphino)pentane, 3a ; and 2,3-bis(-bis(-p-N,N-dimethylaminophenyl)phosphino) butane, 4a ; and their N-protonated and N-Me quaternized analogues are reported. The ligands comprise a versatile set which can be used both in organic and aqueous solvents. A detailed investigation of solvent and substituent effects is provided. The presence of p-NMe 2 groups enhances the rate of reaction in all cases. For the DIOP derivative, 2a , the presence of the dimethylamino group causes a reversal in the observed dominant product antipode. This is attributed predominantly to a change in preferred ligand conformation rather than to a kinetic difference between the two diastereomers of a single ligand conformation.

Aromatization of n-hexane by platinum-containing molecular sieves I. Catalyst preparation by the vapor phase impregnation method

A vapor phase impregnation method with Pt(acac){sub 2} has been developed and used to load Pt into aluminosilicate (KL, BaKL, NaY, CsNaY, cubic and hexagonal polytypes of faujasite, ZSM-12, and SSZ-24) and aluminophosphate (AlPO{sub 4}-5 and VPI-5) molecular sieves. Pt-containing molecular sieves are characterized by XRD,TPD, elemental analysis, {sup 13}C MAS NMR, TEM, and H{sub 2} chemisorption. {sup 13}C MAS NMR, TEM, and H{sub 2} chemisorption measurements reveal that Pt can be loaded into the micropores of molecular sieves with both charged and neutral frameworks. Pt impregnated into zeolites and aluminophosphates by this method does not migrate to the exterior surface of the molecular sieve catalysts at n-hexane aromatization reaction conditions of atmospheric pressure and temperatures between 460 and 510 C.

Bis[tris(m(sodium sulfonato)phenyl)phosphine] hexacarbonyl dicobalt, Co2(CO)6 (P(m-C6H4SO3Na)3)2, in a supported aqueous phase for the hydroformylation of 1-hexene

Abstract The synthesis of the cobalt carbonyl phosphine complex, Co2(CO)6(P(m-C6H4SO3Na)3)2, is described and the complex is used as a catalyst for the hydroformylation of 1-hexene under two-phase and supported aqueous phase reaction conditions. Under two-phase reaction conditions both with and without excess phosphine substantial quantities of cobalt are leached into the organic phase and the observed activity is consistent with catalysis from HCo(CO)4 in the organic phase. When the complex is supported onto the controlled pore glass CPG-340 in a supported aqueous phase configuration the amount of cobalt lost into the organic phase is minimized and the observed activity appears to come from the complex on the glass. When excess phosphine as well as the complex are supported on the glass cobalt leaching is further reduced under batch reaction conditions.

A comparison of X and Y zeolite-supported rhodium as propylene hydroformylation catalysts

A direct comparison of rhodium-exchanged zeolites X and Y as vapor-phase propylene hydroformylation catalysts is reported. Hydrogenation and hydroformylation occur simultaneously over these catalysts in a reactant stream consisting of propylene:H2:N2:CO (3:3:2:1) at atmospheric pressure. Selectivity to n-butyraldehyde versus iso-butyraldehyde is 2.0:1 and 1.9:1 for rhodium on X and rhodium on Y, respectively. Similar hydroformylation activation energies are obtained, while hydrogenation activation energies are somewhat different. Infrared spectroscopy shows the presence of a geminal dicarbonyl, Rh(CO)2+, on zeolite X and Rh6(CO)16 on zeolite Y after hydroformylation.

High resolution, quasi-equilibrium sorption studies of molecular sieves

Argon, nitrogen, and neopentane adsorption isotherms from molecular sieves are recorded at 87 K, 77 K, and 273 K, respectively, by a quasi-equilibrium, high resolution gas sorption technique. The molecular sieves used in this study are alkali exchanged zeolite X, AlPO4-11, AlPO4-5, VPI-5, KL, CaA, ZSM-5, and ZSM-11. Little relation is observed between the transition pressure for microporous nitrogen adsorption and pore size. Small changes in the effective pore size resulting from variations in cation size are detected in the transition pressure for argon adsorption. Large shifts in the transition pressure for argon adsorption are found for the 10-, 12-, and 18-membered ring pores of AlPO4-11, AlPO4-5, and VPI-5, respectively. Argon adsorption combined with neopentane adsorption on microporous materials provides additional information regarding transitions in the isotherm that result from dual pore systems and effects that may be due to adsorbate packing. The step in the nitrogen isotherm atP/P0> 0.1 from ZSM-5 is not observed in the nitrogen isotherm from ZSM-11.