DOI: 10.1002/cctc.201100161 Au on Nanosized NiO: A Cooperative Effect between Au and Nanosized NiO in the Base-Free Alcohol Oxidation Alberto Villa, [a] Carine E. Chan-Thaw, [a] Gabriel M. Veith, [b] Karren L. More, [b] Davide Ferri, [c] and Laura Prati* [a] Introduction Developing catalysts that utilize molecular oxygen, but do not overoxidize or leach while maintaining a high catalytic efficien- cy, is a fundamental challenge to the development of aqueous heterogeneous catalysts. Au catalysts are widely investigated because they overcome these challenges; however, they are often operated under alkaline conditions, which are believed to facilitate the first step of the oxidative dehydrogenation (H abstraction), making purification a challenge and limiting their industrial usefulness. [1] It is possible to circumvent the direct use of a base through the use of basic supports, such as carbo- nates or hydrotalcite. [2–4] In this work, we demonstrate a new way to increase activity without a base. We show an order of magnitude increase in the base-free liquid phase oxidation ac- tivity of supported gold catalysts as the size of the NiO support material is reduced from micrometers to nanometers. A similar effect has been detected for CO oxidation over Au supported on nanosized ZrO 2 . [5] In that case, the reason was attributed to an improvement in the Au–ZrO 2 contact through the creation of a Au–ZrO 2 junction. In the present study, we demonstrate that in the liquid phase oxidation of alcohols, in which the basic properties of the support are of importance, the reduc- tion of the support on the nanometric scale greatly improves the activity of the catalyst, not only because of the increase in the basicity of the support, but also because of a cooperative effect between Au and NiO. Au on even more basic supports (e.g., MgO) shows a lower activity than did Au/nNiO (nano- sized NiO). Instead, support chemistry plays a critical role in the observed catalytic properties. Furthermore, this activity is 10 times greater than that of gold catalysts supported on typi- cal supports, such as activated carbon (AC) and TiO 2 . Recently, Ni-based materials have received a lot of attention owing their intrinsic basicity (isoelectric point = 9.3–10.3). [6] For example, Ru supported on Ni(OH) 2 is 5000 times more active than Ru/C or Ru/TiO 2 in the oxidation of alcohols. [7] Results and Discussion Au catalysts were synthesized by employing a previously de- scribed procedure of sol immobilization that uses Au–polyvinyl alcohol-protected nanoparticles with a mean diameter of 2.5 nm. [8] The catalytic test was carried out in cyclohexane as the solvent (alcohol/cyclohexane = 50:50 wt/wt, alcohol/ metal = 1000 mol/mol, pO 2 = 0.3 MPa, T = 80 8C). The catalytic performance of Au/nNiO was compared with that of Au nano- particles supported on Ni(OH) 2 , bare nNiO, commercial NiO, and more classical supports for Au, such as AC, TiO 2 , MgO, SiO 2 , and H-mordenite (Figure 1). According to literature reports, nNiO is an active catalyst for the oxidation of benzyl alcohol, which reaches a conversion of 5 % after 6 h. [9] The addition of gold to nNiO resulted in the most active catalyst, which reached a conversion of 55 % after 6 h (Table 1), one order of magnitude higher than the conver- sion of all the other catalysts tested ( 6 %), except for Au on H-mordenite, which showed a conversion of 14 %. The Au/H- mordenite catalyst was shown to have a peculiar activity for the base-free oxidation of glycerol. [10] The selectivity to alde- hyde was also affected by the basicity of the support, which promoted the overoxidation of alcohols to acids. In the case of a basic support (nNiO and MgO), the selectivity to aldehyde decreased from 95–97% to 65–68% (Table 1). The stability of the catalyst was also evaluated in a recycling experiment (time of reaction 10 h), in which the catalyst of the first run was recovered by centrifugation and reused in the fol- Nanosized NiO has been synthesized and used as a support for polyvinyl alcohol-protected Au nanoparticles. This catalytic system exhibits an extraordinary performance in the base-free liquid phase oxidation of alcohols compared to the same Au supported on a commercial, micrometersized NiO. This en- hancement in activity cannot be solely attributed to the im- proved basic properties of the support. A cooperative effect between Au nanoparticles and nanosized NiO is envisaged. [a] Dr. A. Villa, Dr. C. E. Chan-Thaw, Prof. L. Prati Department of Inorganic Chemistry L. Malatesta Università degli studi di Milano, via Venezian 21, 20133 Milano (Italy) Fax: (+ 39) 02503-14405 E-mail : Laura.Prati@unimi.it [b] Dr. G. M. Veith, Dr. K. L. More Materials Science and Technology Division Oak Ridge National Laboratory, Oak Ridge, TN 37831 (USA) [c] Dr. D. Ferri Empa – Materials Science & Technology Überlandstrasse 129, 8600 Dübendorf (Switzerland) 1612  2011 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim ChemCatChem 2011, 3, 1612 – 1618