Unique CO methanation catalysts comprising bimetallic Ni-Rh nanoalloy/3DOM LaAlO have been successfully prepared via a poly(methyl methacrylate) microsphere colloidal crystal-templating route, followed by the in situ growth of Ni nanoparticles (NPs). Here, we show that unlike traditional Ni particles deposited on a perovskite support, the exsolution of Ni occurs on both the external and internal surface of the porous perovskite substrate, leading to a strong metal-support interaction. Owing to the exsolution of Ni and the formation of Ni-Rh nanoalloys, a 52% enhancement in the methanation turnover frequency was obtained over the Ni-Rh/3DOM LaAlO [13.9 mol/(mol h)] compared to Rh/3DOM LaNiAlO [9.16 mol/(mol h)] before reduction treatment. The results show that the low-temperature reducibility, rich surface adsorbed oxygen species, and basic sites of the catalyst greatly improve its activity toward CO methanation. The hierarchically porous structure of the perovskite support provides a high dispersion of bimetallic Ni-Rh NPs.

Semiconducting single-walled carbon nanotubes (s-SWNTs) have emerged as a promising class of electronic materials, but the metallic (m)-SWNTs present in all as-synthesized nanotube samples must be removed for many applications. A high selectivity and high yield separation method has remained elusive. A separation process based on selective chemistry appears to be an attractive route since it is usually relatively simple, but more effective chemicals are needed. Here we demonstrate the first example of a new class of dual selective compounds based on polycyclic aromatic azo compounds, specifically Direct Blue 71 (I), for high-purity separation of s-SWNTs at high yield. Highly enriched (~93% purity) s-SWNTs are produced through the simple process of standing arc-discharge SWNTs with I followed by centrifugation. The s-SWNTs total yield is up to 41%, the highest yet reported for a solution-based separation technique that demonstrates applicability in actual transistors. 91% of transistor devices fabricated with these s-SWNTs exhibited on/off ratios of 10(3) to 10(5) with the best devices showing mobility as high as 21.8 cm(2)/V s with on/off ratio of 10(4). Raman and X-ray photoelectron spectroscopic shifts and ultraviolet-visible-near-infrared (UV-vis-NIR) show that I preferentially complexes with s-SWNTs and preferentially suspends them. Preferential reaction of naphthyl radicals (generated from I with ultrasonication) with m-SWNTs is confirmed by changes in the D-band in the Raman spectroscopy, matrix-assisted desorption-ionization time-of-flight mass spectrometry (MALDI-TOF-MS), and molecular simulation results. The high selectivity of I stems from its unique dual action as both a selective dispersion agent and the generator of radicals which preferentially attack unwanted metallic species.

Pure semiconducting single-walled carbon nanotubes (SWNTs) are appealing for many electronic circuits and devices, but the presence of parasitic metallic SWNTs in all as-synthesized nanotube samples makes this application elusive. Agarose gel electrophoresis (AGE) can be used to separate metallic from semiconducting SWNTs when applied in conjunction with the use of an appropriate surfactant or dispersant. To date, only sodium dodecyl sulfate (SDS) has been reported to permit considerable separation with AGE. In this study, we report on the considerably better separation achieved using chondroitin sulfate (CS-A) as a dispersant in AGE compared with SDS-assisted AGE. The CS-A assisted AGE technique may be used to produce in a single pass semiconducting SWNTs with purity of 95%, compared with 85% purity achieved with SDS-assisted AGE for the same arc discharge nanotubes. Further, the yield of CS-A assisted AGE is about 25%, which is in the order of 5 to 10 times the yields of other reported highly selective techniques. Semiconducting SWNTs produced via CS-A/AGE were used to fabricate field effect transistors (FET) with mobilities of ∼2 to 8 cm 2 /(V s) and on/off ratios from 10 2 to 10 5 , which are significantly higher than the mobility of 0.7 cm 2 /(V s), and on/off ratio of 10 4 reported for FETs made with semiconducting SWNTs produced by SDS-assisted AGE. The excellent yield-cum-purity single-pass separation is achievable with this unique chemically selective CS-A dispersant with AGE because of its ability to wrap the nanotubes well, high degree of sulfation making the nanotube/CS-A hybrid highly charged and amine functionality resulting in preselectivity of metallic nanotubes, causing the latter to migrate much more effectively under a uniform electric field.

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