Understanding Pore Formation in ALD Alumina Overcoats.

AlOX thin films deposited by atomic layer deposition (ALD) have previously been used to increase both stability and selectivity of supported palladium catalysts and are known to develop nanoscale porosity upon heating. Understanding the factors that affect ALD thin-film porosity enables future design of layered catalytic structures with tunable nanoscale features on industrially-relevant high-surface-area materials. In this study, porous and nonporous aluminum oxide supports with and without palladium nanoparticles were overcoated with thin films of 2-7 nm AlOX by ALD deposited at temperatures of 100, 200, and 300 °C. Hydroxyl loss and changes in surface chemistry were observed upon heating the films, and changes in surface area and pore volume of the annealed films were correlated to AlOX deposition temperature and the presence of Pd. Crystallization of the overcoat to γ-Al2O3 is shown to occur separately from hydroxyl loss and pore formation. A mechanistic understanding of pore formation in AlOX ALD films is obtained by reference to studies of the structural transformations accompanying the formation of transition aluminas from hydroxide precursors. Additionally, a direct and tunable correlation is established between pore development and the overall hydroxyl content of AlOX ALD coatings.

A Single-Source Precursor Approach to Self-Supported Nickel-Manganese-Based Catalysts with Improved Stability for Effective Low-Temperature Dry Reforming of Methane.

Self-supported nickel-manganese-based catalysts were synthesized from heterobimetallic nickel manganese oxalate precursors via a versatile reverse micelle approach. The precursors were subjected to thermal degradation (400 °C) in the presence of synthetic air to form respective metal oxides, which were treated under hydrogen (500 °C) to form Ni2 MnO4 -O2 -H2 , Ni6 MnO8 -O2 -H2 and NiO-O2 -H2 . Similarly, the precursors were also treated directly under hydrogen at the same temperature to form Ni2 MnO4 -H2 and Ni6 MnO8 -H2 . The catalysts were extensively investigated by PXRD, SEM, TEM, XPS and BET analyses. The resulting catalysts were applied for dry reforming of methane (DRM) and exhibit better stability and resistance to coking than coprecipitated catalysts. Further, we show that addition of manganese, which is not an active catalyst for DRM alone, to nickel has a significant promotion effect on both the activity and stability of DRM catalysts, and a Ni/Mn ratio lower than 6:1 enables optimized activity for this system.

Nanostructured manganese oxides as highly active water oxidation catalysts: a boost from manganese precursor chemistry.

We present a facile synthesis of bioinspired manganese oxides for chemical and photocatalytic water oxidation, starting from a reliable and versatile manganese(II) oxalate single-source precursor (SSP) accessible through an inverse micellar molecular approach. Strikingly, thermal decomposition of the latter precursor in various environments (air, nitrogen, and vacuum) led to the three different mineral phases of bixbyite (Mn2 O3 ), hausmannite (Mn3 O4 ), and manganosite (MnO). Initial chemical water oxidation experiments using ceric ammonium nitrate (CAN) gave the maximum catalytic activity for Mn2 O3 and MnO whereas Mn3 O4 had a limited activity. The substantial increase in the catalytic activity of MnO in chemical water oxidation was demonstrated by the fact that a phase transformation occurs at the surface from nanocrystalline MnO into an amorphous MnOx (1