Textural and Structural Analyses of Industrial Raney Nickel Catalyst Cristiane B. Rodella, Guinther Kellermann, Maria Suzana P. Francisco, Maura H. Jorda ˜o, and Daniela Zanchet* Laborato ´rio Nacional de Luz Sı ´ncrotron (LNLS), C.P. 6192, 13083-970, Campinas SP, Brazil In this work, the influence of the temperature (60, 80, and 110 °C) in the production of Raney Ni catalysts was addressed. The catalysts were obtained by alkaline leaching of a Ni-Al alloy, and both the Ni-Al alloy and the leaching process that was evaluated were provided by an industrial partner. The physical-chemical properties of the catalysts were investigated by X-ray diffraction (XRD), scanning and transmission electron microscopies (FEG-SEM and TEM), X-ray photoelectron spectroscopy (XPS), N 2 adsorption, and small- angle X-ray scattering (SAXS) techniques. In particular, a comparison between SAXS and N 2 adsorption results about the textural properties is discussed. The three Raney Ni catalysts presented the typical highly porous metallic nickel structure. The analysis of the surface, however, suggested the presence of major contributions of NiO, Ni(OH) 2 /Ni 2 O 3 , and Ni-O-Al species in all samples and the presence of Ni 0 for the samples produced at 60 and 80 °C. The two samples prepared at lower temperatures presented similar characteristics: crystalline domains of 50 and 60 Å, BET specific surface area of 58 and 65 m 2 g -1 , and porosity of 0.100 and 0.107 cm 3 g -1 , respectively. These properties appear to be more interesting for catalytic purposes than the characteristics of the catalyst prepared at 110 °C: mean crystalline size of 100 Å, BET specific surface area of 51 m 2 g -1 , and pore volume of the 0.097 cm 3 g -1 . A higher concentration of Al species, about 80 atom %, however, was also observed on the surface of the catalysts produced at 60 and 80 °C. The larger pores found in the catalyst produced at 110 °C may have facilitated the removal of the Al species during the washing process and are probably related to the larger Ni crystalline domains in this sample. 1. Introduction Raney Ni catalyst is widely used as a heterogeneous catalyst for liquid-phase hydrogenation reactions, 1-3 being extensively applied in industry for hydrogenation of D-glucose to sorbitol. 4 The catalyst is produced by alkaline leaching of aluminum from Ni-Al alloy (usually 50-50 wt %), which consists of Ni 2 Al 3 and NiAl 3 intermetallic phases and pure Al. The leaching process leads to the formation of interconnected metallic nickel nano- particles forming a highly porous spongelike structure. 4 As shown in previous works, 1-9 some parameters in the preparation of Raney Ni catalyst can affect its final textural and structural characteristics and, consequently, its catalytic properties. The microstructure of the Ni-Al precursor alloy seems to be the most important factor. 5-9 The intermetallic phases do not exhibit the same reactivity in alkaline solution and the leaching rate increases from NiAl 3 to Ni 2 Al 3 phase. 5,10,11 Besides that, the temperature, time, and concentrations used in the leaching process have a remarkable effect on the textural properties of the catalyst. 6-9 For example, the specific surface area and total pore volume of the Raney Ni catalyst tend to decrease with increasing leaching temperature, while the mean pore diameter becomes larger. 6,7 The N 2 adsorption technique is widely used to characterize the specific surface area and porosity of porous materials such as catalysts and it is based on the adsorption of the N 2 molecules (absorbate) on the surface of the solid (adsorbent) at low pressure and temperature (-196 °C). By increasing the pressure, a complete coverage of the specific surface area of the material is achieved, and the pores are filled by N 2 molecules. An alternative technique to extract information about the surface area and porosity of the materials in the 10-500 Å range is small-angle X-ray scattering (SAXS). The SAXS intensity arises from the electron density inhomogeneites in the nanometric size range and has been widely used in the investigation of different types of materials. 13-16 An advantage of the SAXS technique is the possibility to obtain information on closed pores in addition to the nitrogen-accessible pores. In addition, in situ measurements can be performed, probing the evolution of the materials under different conditions. 17 In the present work, the influence of the leaching temperature on the final textural and structural characteristics of industrial Raney Ni catalysts was evaluated. This study compiles essential information and conclusions concerning a process that was of interest industrially. The catalysts were prepared by alkaline dissolution of aluminum from the Ni-Al alloy at three different temperatures (60, 80, and 110 °C). While the textural properties of the final material were analyzed by N 2 -adsorption and SAXS techniques, the crystallographic phases and surface compositions were determined by X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. Complementary analyses of the morphology of the catalysts were performed by transmission and scanning electron microscopies (TEM and FEG-SEM, respectively). 2. Experimental Section 2.1. Sample Preparation. The Ni-Al precursor alloy of Raney Ni catalysts was provided by GETEC Guanabara Quı ´mica Industrial S.A. (Rio de Janeiro, Brazil). The chemical analysis by X-ray fluorescence spectroscopy (XRF) showed that the Ni-Al alloy contained 51.3 wt % Ni and 48.7 wt % Al. The Raney Ni catalysts were prepared by adding the Ni-Al alloy to a 25 wt % NaOH aqueous solution under stirring. During the leaching process, the temperature was kept constant at 60, 80, or 110 °C. Since the reaction of the Ni-Al alloy with an aqueous hydroxide is highly exothermic, the Ni-Al alloy was added slowly and in small quantities to keep the * To whom correspondence should be addressed. Tel: +55 19 3512 1049. Fax: +55 19 3512 1004. E-mail: zanchet@lnls.br. Ind. Eng. Chem. Res. 2008, 47, 8612–8618 8612 10.1021/ie800543t CCC: $40.75  2008 American Chemical Society Published on Web 10/22/2008