A. Frydman

A study of the promoting effect of noble metal addition on niobia and niobia alumina catalysts

The catalytic activity of Nb 2 O 5 and Nb 2 O 5 /Al 2 O 3 -supported metal catalysts was evaluated in the n-heptane conversion, CO hydrogenation and butadiene hydrogenation. After high temperature of reduction (HTR), the metal adsorption capacity decreases on all the samples, due to the reduction of Nb 2 O 5 with subsequent blocking of metal atoms and bimetallic effect. It was also observed that the activity decay caused by metal-support interaction was remarkably inhibited on the bimetallics with respect to the monometallics by comparing reaction rates after HTR. Thus, the addition of Rh to Co, Cu to Pd and Sn to Pt on niobia catalysts significantly altered the product distribution in Fischer-Tropsch synthesis (FTS) and in the hydrogenation and dehydrogenation of hydrocarbons, respectively. In addition, an unusual bifunctional effect was obtained in Pt/Nb 2 O 5 /Al 2 O 3 catalyst.

The promoting effect of noble metal addition on niobia-supported cobalt catalysts

Abstract The promoting effects of a noble metal (Pd, Pt, Rh) added to Co/Nb 2 O 5 catalysts were studied by varying the Me/Co atomic ratios. Acid niobium was calcined to niobium pentoxide. The surface and bulk structures of the calcined materials were characterized by XPS and TPR techniques. The catalytic performance was obtained with CO hydrogenation. The addition of a noble metal promoted the reduction of Co 3+ and Co 2+ phases at the surface. XPS results revealed that Co 2+ species are well dispersed as a thin layer around the niobium support together with Co 3 O 4 crystallites islands. The CO 3 O 4 /Co 2+ ratio depends on the surface area of the support. XPS measurements also revealed that PdO, Rh 2 O 3 and PtO 2 are the main phases in the mono and bimetallic catalysts. The activity of the bimetallic catalysts increased and the stability was already attained. The selectivities towards C 5 + and oxygenates increased with the addition of Rh up to an atomic ratio of 0.5 and decreased beyond that. This behavior is similar for both temperatures of reduction at 573 and 773 K.

Effect of preparation method on 5% Co/Nb2O5 in Fischer-Tropsch Syntesis (FTS)

Abstract Three preparation methods of 5% Co/Nb2O5 were studied : Incipient wetness impregnation, deposition-precipitation with and without aging. Its effects over total area, mean pore diameter, cobalt species and acidity of reduced catalysts were investigated by BET, Hg porosimetry, XRD, DRS, TPR, TPO and NH3 TPD. TPR results showed that the reduction proceeds as two steps (Co+3 → Co+2 → Coo). TPR and DRS indicated the presence of Co+2 in the precipitated catalysts. The main phase was Co3O4 in all catalysts. The FTS selectivity showed good correlation with the strong acidity.

High Selectivity of Diesel Fraction in Fischer-Tropsch Synthesis with Co/Nb2O5

Abstract The Fischer–Tropsch Synthesis (FTS) was studied on a 10%Co/Nb2O5 at 493 K and total pressures of 0.1 and 3.0 MPa. The results at 3.0 MPa indicated high selectivity of linear hydrocarbons in diesel range (C13–C18). Chains growth deviated considerably from Anderson–Schulz–Flory behaviour above C13. TPO analysis showed structural modifications of the catalyst after 24 h on stream.

Determination of Thermal Properties of Solid Porous Media on a Single-Blow Testing Apparatus

The efficiency of regenerative cycle refrigerators greatly depends upon the high performance of the regenerator. The design of high performance cryogenic regenerators is a challenge because several variables must be competitively balanced. Using published correlations, it is relatively easy to design extremely high performance regenerators but there are numerous manufacturing realities that limit observed regenerator performance. A methodology is presented to evaluate solid porous matrices that differ in nature and geometry, by balancing the effective thermal conductivity, heat transfer coefficient and friction factor. We have designed and built a single-blow testing apparatus to measure the design parameters for different porous solid matrices, by flowing a heated fluid through it and recording the temperature profiles as a function of time and location, for different values of Reynolds Number.1 The determination of these parameters is obtained by fitting the experimental profiles with theoretical profiles from the solution of the energy balance equations in the fluid-solid system. Here, we present the results obtained on Dysprosium sphere particles with average particle size of 288 μm, as an initial demonstration of a characterization and testing methodology for high performance regenerator matrices. Important considerations with respect to the longitudinal conductance are also made.

A laboratory apparatus to determine fluid-solid heat transfer coefficient and effective thermal conductivity of solid porous media

A single-blow apparatus was designed and built to specifically eliminate most systematic errors in characterizing thermal properties of solid porous media. By matching temperature profiles calculated from the solid-fluid transient energy balance in a porous bed to experimental profiles, the heat transfer coefficient between solid and fluid and the effective longitudinal thermal conductivity can be determined. The specifications of such an apparatus require strict accounting of sources of heat leak and other systematic errors. Here, we present a detailed study in identifying and minimizing these systematic errors. Details on the design, construction and testing of this apparatus are shown, including utilization of low thermal conductivity materials for components, and meticulous design and construction of temperature probes. We also present for the first time a methodology to correct for parasitic heat leaks inherently present in the system. This correction procedure to correct the temperature profiles eliminates the effect of the major systematic errors. This apparatus is being used as a screening-design tool to characterize overall effectiveness of high performance regenerators for regenerative cycle refrigerators and liquefiers.