Graphite oxide (GO) and its derivatives have been studied using 13C and 1H NMR. NMR spectra of GO derivatives confirm the assignment of the 70 ppm line to C−OH groups and allow us to propose a new structural model for GO. Thus we assign the 60 ppm line to epoxide groups (1,2-ethers) and not to 1,3-ethers, as suggested earlier, and the 130 ppm line to aromatic entities and conjugated double bonds. GO contains two kinds of regions:  aromatic regions with unoxidized benzene rings and regions with aliphatic six-membered rings. The relative size of the two regions depends on the degree of oxidation. The carbon grid is nearly flat; only the carbons attached to OH groups have a slightly distorted tetrahedral configuration, resulting in some wrinkling of the layers. The formation of phenol (or aromatic diol) groups during deoxygenation indicates that the epoxide and the C−OH groups are very close to one another. The distribution of functional groups in every oxidized aromatic ring need not be identical, and both the oxidized rings and aromatic entities are distributed randomly.

No abstract

Formic acid (FA) has tremendous potential as a safe and convenient source of hydrogen for sustainable chemical synthesis and renewable energy storage, but controlled and efficient dehydrogenation of FA by a robust solid catalyst under ambient conditions constitutes a major challenge. Here, we report that a previously unappreciated combination of subnanometric gold and an acid-tolerant oxide support facilitates the liberation of CO-free H(2) from FA. Applying an ultradispersed gold catalyst comprising TEM-invisible gold subnanoclusters deposited on zirconia to a FA-amine mixture affords turnover frequencies (TOFs) up to 1590 per hour and a turnover number of more than 118,400 at 50 °C. The reaction was accelerated at higher temperatures, but even at room temperature, a significant H(2) evolution (TOFs up to 252 h(-1) after 20 min) can still be obtained. Preliminary mechanistic studies suggest that the reaction is unimolecular in nature and proceeds via a unique amine-assisted formate decomposition mechanism on Au-ZrO(2) interface.

A golden opportunity: A highly robust catalyst system consisting of gold nanoparticles supported on acid‐tolerant ZrO2 promoted the conversion of biomass‐derived levulinic acid (1) and formic acid (2) into γ‐valerolactone without the use of an external H2 supply (see scheme, red). The Au/ZrO2 catalyst was also used for the direct one‐pot synthesis of highly valuable pyrrolidone derivatives from 1, 2, and primary amines (see scheme, blue).

Powder X-ray diffraction (XRD), 29Si magic-angle-spinning (MAS) NMR spectroscopy, and transmission electron microscopy (TEM) as well as N2 adsorption have been employed to study the formation of various mesophases that lead to the synthesis of cubic mesoporous MCM-48 molecular sieve. A typical synthesis is performed at 373 K, pH = 11.8 using tetraethyl orthosilicate as the silicon source and cetyltrimethylammonium bromide (CTAB) as the structure-directing agent with a molar gel composition of 1:0.23:0.55:112SiO2/Na2O/CTAB/H2O. XRD shows that a disordered tubular mesophase (H1) rapidly forms and then transforms to a layered phase (L1) upon heating at 373 K for 5−10 h. After the hydrothermal treatment continues for 72 h, the layered phase (L1) gradually transforms to a cubic MCM-48 mesophase (V), which is accompanied by a slight pH increase of about 0.2 units. Prolonged hydrothermal treatment for over 120 h results in further structural transformation from the cubic mesophase V to a second layered phase (L2). 29Si MAS NMR reveals that the L2 layered phase has a more regular atomic arrangement than the other three mesophases. However, the silica condensation increases monotonicly in the order H1 → L1 → V → L2 with hydrothermal treatment time. The cubic MCM-48 mesophase is not completely stable under hydrothermal synthesis conditions since it converts to the L2 phase. This may account for the poor repeatability of prior syntheses of MCM-48 material. We show that cubic MCM-48 can be stabilized either by addition of acetic acid to maintain a constant gel pH or by selection of the reaction time to prevent further mesophase transformation. TEM and N2 adsorption data show well-defined three-dimensional channels for the cubic MCM-48.