Cross-shaped and octahedral nanoparticles (hexapods) of MnO in size, and fragments thereof, are created in an amine/carboxylic acid mixture from manganese formate at elevated temperatures in the presence of water. The nanocrosses have dimensions on the order of 100 nm, but with exposure to trace amounts of water during the synthesis process they can be prepared up to about 300 nm in size. Electron microscopy and X-ray diffraction results show that these complex shaped nanoparticles are single crystal face-centered cubic MnO. In the absence of water, the ratio of amine to carboxylic acid determines the nanocrystal size and morphology. Conventionally shaped rhomboehdral/square nanocrystals or hexagonal particles can be prepared by simply varying the ratio of tri-n-octylamine/oleic acid with sizes on the order of 35-40 nm in the absence of added water. If the metal salt is rigorously dried before the synthesis, then "flower-shaped" morphologies on the order of 50-60 nm across are observed. Conventional squareshaped nanocrystals with clearly discernible thickness fringes that also arise under conditions producing the nanocrosses mimic the morphology of the cross-shaped and octahedral nanocrystals and provide clues to the crystal growth mechanism(s), which agree with predictions of crystal growth theory from rough, negatively curved surfaces. The synthetic methodology appears to be general and promises to provide an entryway into other nanoparticle compositions.

The concurrent propagation of the aromatics-based and olefins-based catalytic cycles at early stages of the methanol-to-olefins reaction over HSAPO-34 and the resulting consequences on light olefins selectivities are demonstrated with 13 C 3-propylene/ 12 C 2-dimethyl ether isotopic tracing studies at 623 K and sub-complete dimethyl ether conversions. Transients in effluent product selectivities were rationalized by the maturation of the entrained hydrocarbon pool where catalyst turnover number is introduced as a compendious descriptor of reaction progress. The distinct 13 C-content of ethylene from other effluent products and its agreement with the 13 C-contents of entrained polymethylbenzenes indicate that ethylene is a product of aromatics-based dealkylation events while the match between methylationpredicted and experimentally observed 13 C-contents for C 5+ olefins establishes that they are products of olefins-based methylation events. Methanol-to-olefins conversion proceeds through a dual cycle mechanism proposed earlier for methanol conversion over other solid acid catalysts where the topology of HSAPO-34 specifically engenders the prevalence of the aromatics-based cycle at >∼200 mol C mol −1 H + catalyst turnovers.

The conversion of hexagonal-, square-, and cross-shaped MnO nanoparticles into mixed MnO-Mn 3 O 4 nanoparticles occurs with retention of the nanoparticle shape. Upon aging, extra diffraction spots appear in the TEM analyses of both hexagonal-and cross-shaped nanoparticles (NPs). These extra diffraction spots can be assigned to the spinel form of Mn 3 O 4 (s-Mn 3 O 4 ) and exhibit moiré interference patterns arising from the presence of two closely aligned, crystallographically similar phases. Examination of a variety of reaction conditions showed that the transformation of MnO into MnO/Mn 3 O 4 occurred while the particles are suspended in hexane at ambient temperature, by refluxing in hexadecane for 36 h, by heating to 200°C in air, and by irradiating the NPs with a Raman laser beam. The crystal phase development and shape retention can be observed by using transmission electron microscopy (TEM). Single-crystal and polycrystalline selected area electron diffraction (SAED) patterns and dark-field TEM images confirm the coexistence of both MnO and s-Mn 3 O 4 phases. Evaluation of the polycrystalline SAED patterns after irradiation in the Raman spectrometer indicated the presence of rings assignable to the tetragonal phase of Mn 3 O 4 (t-Mn 3 O 4 ) as well as MnO and s-Mn 3 O 4 . The growth of the tetragonal phase by laser heating in the Raman experiment was confirmed by powder X-ray diffraction.