Tungsten-incorporated 3D mesoporous silicates, W-KIT-6, W-KIT-5, and W-SBA-16 catalysts, outperform supported tungsten oxide catalysts (WO 3 /SiO 2 and WO 3 /KIT-6) for the metathesis of ethylene and 2-butene to propene at 450°C. All catalysts exhibit steady activity and stability during 7 h runs in a fixed-bed reactor. Furthermore, on all mesoporous catalysts, a maximum propylene yield was obtained at an optimum W loading at which the catalyst acidity is also maximum. Slightly delayed addition of the W source during the one-pot synthesis protocol markedly improves the propene yield on W-KIT-6 catalyst. XPS results conclusively show that this enhancement is due to preferential enrichment of active W species on the catalyst surface. Extended runs lasting five days reveal very little loss of activity even which is easily recovered by calcination in air.

A zirconium-incorporated Ia3d cubic three-dimensional (3-D) mesoporous silicate, KIT-6, with different zirconium loadings, was synthesized via a one-step direct hydrothermal synthesis procedure employing Pluronic P123 triblock copolymer as the structure-directing agent under acidic conditions. Various characterization techniques, such as two-dimensional (2-D) small-angle X-ray scattering (SAXS), nitrogen sorption, temperature-programmed desorption of ammonia (NH3-TPD), and ultraviolet–visible-light (UV-Vis) spectra, showed that zirconium was incorporated as Zr4+ ions in the KIT-6 framework, which retained the structural integrity with a highly ordered pore structure. The Zr-KIT-6 materials exhibit very high surface areas (810–980 m2/g) and large pore volumes (1.07–1.65 cm3/g) that decrease with an increase in zirconium content. In contrast, the pore size distribution remains relatively unaffected by zirconium loading with an average pore diameter of ∼9.3 nm. The Zr-KIT-6 materials possess Lewis acidity that increases with zirconium loading. In the 180–300 °C range, the Zr-KIT-6 materials are shown to be highly active for the test reaction of isopropanol (IPA) dehydration to propylene (selectivity >98%). The activation energy for IPA dehydration, estimated from intrinsic rate constants normalized with respect to the Lewis acid sites, was ∼49 ± 1 kJ/mol and found to be lower than most other Brønsted or Lewis acidic heterogeneous catalysts reported in the literature for IPA dehydration. Furthermore, these catalysts showed nearly stable activity with very little deactivation during extended runs at 260 and 300 °C.

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A novel process for continuous hydroformylation in CO2‐expanded liquids (CXLs) is demonstrated using bulky phosphite ligands that are effectively retained in the stirred reactor by a nanofiltration membrane. The reactor is operated at 50°C with a syngas pressure of 0.6 MPa to avoid CO inhibition of reaction rate and selectivity. The nanofiltration pressure is provided by ∼3.2 MPa CO2 that expands the hydroformylation mixture and increases the H2/CO ratio in the CXL phase resulting in enhanced turnover frequency (∼340 h−1), aldehydes selectivity (>90%) and high regioselectivity (n/i ∼8) at nearly steady operation. The use of pressurized CO2 also reduces the viscosity in the CXL phase, thereby improving the mass‐transfer properties. Constant permeate flux is maintained during the 50 h run with Rh leakage being less than 0.5 ppm. This technology concept has potential applications in homogeneous catalytic processes to improve resource utilization and catalyst containment for practical viability. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4287–4296, 2013

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