Comparison Between Microstructures of Conventional and New Raney Catalysts

Abstract

Raney-type catalysts are widely applied in a variety of commercial processes in the chemical industries. Conventionally, Raney nickel catalysts are produced by leaching aluminum from cast Al-Ni alloys; they consist of porous nickel particles having small amounts (3-5 wt. %) of residual aluminum and surface areas in the range of 50-130 m 2 /g [1]. In recent years, reports have been made regarding the production of Raney catalysts by leaching of precursor alloys obtained by mechanical alloying (MA) [2][3][4]. In these studies, the microstructural characterization has been quite limited in detail. The results of our own work with Raney nickel and nickel-iron catalysts have clearly shown that, compared to conventional Raney catalysts, those derived from precursor alloys prepared by MA possess important advantages regarding simplicity and reproducibility of production, as well as catalytic performance. In order to better understand these findings, we have now conducted a comparative microstructural characterization of conventional and MA Raney catalysts.Catalyst preparation has been reported elsewhere [3,4]. Materials characterized in the present study included the as-milled MA alloys before and after leaching. For comparison, it was included a commercial Raney nickel catalyst. All materials were characterized by XRD, SEM, TEM and EDS.Before leaching, the MA powders consisted mainly of nodular particles with sizes mostly in the range 0.5-2 µm (Fig. 1a). The individual particles contained crystallites with sizes mainly in the 5 -10 nm range (not shown). SAD patterns obtained from individual particles gave clear evidence for the existence of the NiAl intermetallic phase, in agreement with the results of XRD.

Molecular modeling and simulation of Raney Nickel: From alloy precursor to the final porous catalyst

“…Over the 10 simulations the final averaged maximum pore diameter is about 43 ± 5 Å. This value is in good agreement with previous experimental results that give a pore diameter between 20 and 100 Å [2,6,18,19]. Similarly the density converges toward an averaged value of 4.1 ± 0.4 g/cm 3 .…”

“…1 and methodology section). For all five structures a density of 4.4 g/cm 3 was obtained which is in accordance with the experimental data of 3.95 g/cm 3 and 4.76 g/cm 3 obtained for NiAl 3 and Ni 2 Al 3 [19]. The cell parameters a, b, and c are each in the same range for m1-m5.…”

“…The converged values of the free volume and surface are close to the higher range of the experimental values that rank between 0.068 and 0.141 cm 3 /g for the free volume [2,6,18,19] and 57 and 120 m 2 /g for the free surface [2,6,18,19], respectively.…”