An infrared study has been conducted on CO 2 sorption into nanoporous CO 2 "molecular basket" sorbents prepared by loading polyethylenimine (PEI) into mesoporous molecular sieve SBA-15. IR results from DRIFTS showed that a part of loaded PEI is anchored on the surface of SBA-15 through the interaction between amine groups and isolated surface silanol groups. Raising the temperature from 25 to 75 °C increased the molecular flexibility of PEI loaded in the mesopore channels, which may partly contribute to the increase of CO 2 sorption capacity at higher temperatures. CO 2 sorption/desorption behavior studied by in situ transmission FTIR showed that CO 2 is sorbed on amine sites through the formation of alkylammonium carbamates and absorbed into the multiple layers of PEI located in mesopores of SBA-15. A new observation by in situ IR is that two broad IR bands emerged at 2450 and 2160 cm -1 with CO 2 flowing over PEI(50)/SBA-15, which could be attributed to chemically sorbed CO 2 species on PEI molecules inside the mesopores of SBA-15. The intensities of these two bands also increased with increasing CO 2 exposure time and with raising CO 2 sorption temperature. By comparison of the CO 2 sorption rate at 25 and 75 °C in terms of differential IR intensities, it was found that CO 2 sorption over molecular basket sorbent includes two rate regimes which suggest two distinct steps: rapid sorption on exposed outer surface layers of PEI (controlled by sorption affinity or thermodynamics) and the diffusion and sorption inside the bulk of multiple layers of PEI (controlled by diffusion). The sorption of CO 2 is reversible at 75 °C. Comparative IR examination of the CO 2 sorption/ desorption spectra on dry and prewetted PEI/SBA-15 sorbent revealed that presorbed water does not significantly affect the CO 2 -amine interaction patterns.

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The effect of synthesis and reaction conditions on the structure and activity of Au clusters supported on nanocrystalline and mesoporous TiO2 was investigated. X-ray absorption spectroscopy was applied to correlate the particle size and the oxidation state with several parameters, such as pH of the precursor solution, Au loading, pretreatment, and support structure. The study using mesoporous TiO2 as the support shows that lower Au loadings resulted in bigger Au aggregates with lower reducibility. The high activity state for Au supported in different allotropic forms of TiO2 corresponds to Au in a fully reduced state. Furthermore, once reduced, no reoxidation occurs under reaction conditions, even after flowing air at higher temperatures (150 and 300 °C). Therefore, our results indicate that oxidized Au is not necessary for high activity. The activity decreased with particle growth, and, compared to the other allotropic TiO2, Au on brookite exhibited no significant particle agglomeration and was the most active catalyst after treatment at 300 °C.

In this paper, a solid molecular basket sorbent, 50 wt% PEI/SBA-15, was studied for CO(2) capture from gas streams with low CO(2) concentration under ambient conditions. The sorbent was able to effectively and selectively capture CO(2) from a gas stream containing 1% CO(2) at 75 °C, with a breakthrough and saturation capacity of 63.1 and 66.7 mg g(-1), respectively, and a selectivity of 14 for CO(2)/CO and 185 for CO(2)/Ar. The sorption performance of the sorbent was influenced greatly by the operating temperature. The CO(2)-TPD study showed that the sorbent could be regenerated under mild conditions (50-110 °C) and was stable in the cyclic operations for at least 20 cycles. Furthermore, the possibility for CO(2) capture from air using the PEI/SBA-15 sorbent was studied by FTIR and proved by TPD. A capacity of 22.5 mg g(-1) was attained at 75 °C via a TPD method using a simulated air with 400 ppmv CO(2) in N(2).

Nanosized anatase (< or = 10 nm), rutile (< or = 10 nm), and brookite (approximately 70 nm) titania particles have been successfully synthesized via sonication and hydrothermal methods. Gold was deposited with high dispersion onto the surfaces of anatase, rutile, brookite, and commercial titania (P25) supports through a deposition-precipitation (D-P) process. All catalysts were exposed to an identical sequence of treatment and measurements of catalytic CO oxidation activity. The as-synthesized catalysts have high activity with concomitant Au reduction upon exposure to the reactant stream. Mild reduction at 423 K produces comparably high activity catalysts for every support. Deactivation of the four catalysts was observed following a sequence of treatments at temperatures up to 573 K. The brookite-supported gold catalyst sustains the highest catalytic activity after all treatments. XRD and TEM results indicate that the gold particles supported on brookite are smaller than those on the other supports following the reaction and pretreatment sequences.

We report the synthesis of NiAu alloy nanoparticles (NPs) and their use in preparing Au/NiO CO oxidation catalysts. Because of the large differences in Ni and Au reduction potentials and the immiscibility of the two metals at low temperatures, [1,2] NiAu alloy NP colloids are inherently difficult to prepare by reducing metal salts with common reducing agents. This study describes the first solution-based synthesis of NiAu alloy NPs by way of a fast butyllithium reduction method. By supporting the particles on SiO 2 and subsequent conditioning, one obtains a NiO-stabilized Au NP catalyst that exhibits remarkable resistance to sintering and is highly active for CO oxidation. The active NiO-stabilized Au NP catalyst is prepared by in situ phase transformation of NiAu alloy NPs through an Au@Ni core-shell-like NP intermediate. In contrast, the corresponding NiO-free Au NPs prepared by an analogous method show negligible low-temperature catalytic activity and a high propensity for coalescence.The development of new bimetallic NP catalysts in various architectures (e.g. alloy, core-shell, aggregates) is receiving increased attention due to the need for more sophisticated, multifunctional catalysts in a variety of applications. [3][4][5][6][7] In comparison to monometallic systems, bimetallic catalysts have the potential advantages of bifunctional activity [8] (e.g. PtRu electrocatalysts), tunable non-native reactivities [5] (e.g. core-shell NPs), and stabilizing influences from a co-metal partner. A classic example of the later is to use certain metal oxides to modify "inactive" silica supports [9] to stabilize and activate small Au NPs for CO oxidation reactions. [10,11] To rationally advance the design of heterogeneous catalysts, systematic analyses of bimetallic architectures and the development of new synthetic methods to make multifunctional catalysts are needed. Herein, we report a new strategy to prepare oxide-stabilized noblemetal NP catalysts using a controlled stepwise phase-separation process of a bimetallic NP precursor. We demonstrate this strategy by making silica-supported NiO-stabilized Au CO oxidation catalysts using an in situ phase separation process of NiAu alloy NP precursor. Because silica is well known to be a poor support for stabilizing Au NPs in catalytic systems, it is an ideal support for evaluating effects of secondary metal oxide components.In the solid state, NiAu alloys can be prepared by high-temperature annealing. [1,2] However, this method produces large particles with small surface areas that limit their application in catalysis. The Ni-Au phase diagram [1,2] shows a solid-solution fcc alloy phase at high temperatures (> 740 8C for 1:1 alloy), but there is a large immiscibility region containing phase-separated fcc Au and fcc Ni at low temperatures. The low-temperature immiscibility of Ni and Au and the large discrepancy in reduction potentials complicate solution-based NiAu alloy preparations. In a previous report, we described a fast butyllithium reduction method for the preparatio...

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