Pyrolusite

About: Pyrolusite is a research topic. Over the lifetime, 819 publications have been published within this topic receiving 10702 citations.

The synthesis of birnessite, cryptomelane, and some other oxides and hydroxides of manganese

Abstract: Detailed methods are described for the laboratory preparation of the manganese minerals manganosite, hausmannite, manganite, partridgeite, birnessite, cryptomelane, pyrolusite, and todorokite New data are presented on the conversion of birnessite to cryptomelane, and on the exchange properties of potassium in these two minerals It was found that the upper limit of potassium in cryptomelane is about 7 % K, while the lower limit lies between 0·25 % and 2·2 % K

The tetravalent manganese oxides: identification, hydration, and structural relationships by infrared spectroscopy

Abstract: A compilation of the infrared powder absorption spectra of most naturally occurring tetravalent and trivalent manganese oxides is presented which is intended to serve as a basis for the spectroscopic identification of these minerals in both ordered and disordered varieties, including those too disordered for X-ray diffraction studies. A variety of synthetic manganese oxides are also included for comparison to the natural phases. The samples include: aurorite, birnessite, braunite, buserite, chalcophanite, coronadite, cryptomelane, groutite, hausmannite, hollandite, lithiophorite, maoganite, manganese(Ill) manganate(IV), manganosite, manjiroite, marokite, nsutite, partridgeite, pyrolusite, quenselite, rancieite, ramsdellite, romanechite, sodium manganese(Il,III) manganate(IV), todorokite, and woodruffite. The spectra indicate that well-ordered water occurs in ramsdellite, chalcophanite, and most romanechites. Disordered water is observed in the spectra of nsutite, hollandites, birnessite, todorokite, buserite, and rancieite. The infrared spectra of well-ordered todorokite, birnessite and rancieite differ which indicates that they possess different structures and should be regarded as distinct mineral species. Much variation is observed in the spectra of pyrolusites, nsutites, birnessites, and todorokites which is interpreted as arising from structural disorder. Spectral trends suggest that todorokite, birnessite and rancieite have layered structures.

Highly efficient heterogeneous photooxidation of 2-propanol to acetone with amorphous manganese oxide catalysts

Abstract: Amorphous manganese oxides, potassium oxalatomanganate complexes, and crystalline tunnel structure manganese oxides (hollandite, todorokite, pyrolusite) have been prepared and used as photocatalysts for the oxidation of 2-propanol to acetone. Amorphous mixed valent manganese oxides, a new class of photocatalytic materials, were the most active catalysts studied at room temperature under visible light illumination. High activities correlate with higher oxidation state manganese (Mn[sup 3+], Mn[sup 4+]) oxides, large surface oxygen concentrations, and the presence of hydroxyl groups on surfaces of these catalysts. BET (surface area analysis), XRD (X-ray diffraction), EDX (energy dispersive X-ray analysis), SEM (scanning electron microscopy), XPS (X-ray photoelectron spectroscopy), and FTIR (Fourier transform infrared) data support these correlations. A mechanism for these photooxidation flow reactions involving manganese oxide catalysts has been proposed. Photochemical and characterization data suggest that the design of active photocatalysts may rely on preparation of mixed valent amorphous oxides that release oxygen more readily than crystalline materials. Conversions as high as 8% and 100% selectivity to acetone have been realized with such systems. 45 refs., 9 figs., 1 tab.