Abstract
AbstractDesigning a stable and selective catalyst with high H2 utilisation is of pivotal importance for the direct gas‐phase epoxidation of propylene. This work describes a facile one‐pot methodology to synthesise ligand‐stabilised sub‐nanometre gold clusters immobilised onto a zeolitic support (TS‐1) to engineer a stable Au/TS‐1 catalyst. A non‐thermal O2 plasma technique is used for the quick removal of ligands with limited increase in particle size. Compared to untreated Au/TS‐1 catalysts prepared using the deposition precipitation method, the synthesised catalyst exhibits improved catalytic performance, including 10 times longer lifetime (>20 days), increased PO selectivity and hydrogen efficiency in direct gas phase epoxidation. The structure‐stability relationship of the catalyst is illustrated using multiple characterisation techniques, such as XPS, 31P MAS NMR, DR‐UV/VIS, HRTEM and TGA. It is hypothesised that the ligands play a guardian role in stabilising the Au particle size, which is vital in this reaction. This strategy is a promising approach towards designing a more stable heterogeneous catalyst.
Highlights
Post-combustion CO2 capture is an important requirement of many industrial processes
NOx is known to have a significant impact on health and the environment, causing the formation of atmospheric ozone and acid (40 μragi·nm.4−3Itaisytehaer)re, floeraedivnitgaltothtahteNfiOttxinegmoisfsNioOnsx are regulated scrubbers to power stations, comprising oxidizing and reducing agents responsible for the conversion of NOx to N2.5 Aqueous alkanolamines have been employed as CO2 capture sorbents, but the presence of NOx was found to result in the irreversible formation of carcinogenic nitrosamines and a capture efficiency.[6−8] Ionic liquids (ILs) have decrease in CO2 been widely investigated for the capture of CO2 as a non-volatile alternative to toxic alkanolamines
Superbase ILs (SBILs) containing an aprotic heterocyclic anion (AHA) were developed to minimize the increase in viscosity observed in amine-functionalized ILs, and they can reversibly capture a greater than equimolar amount of CO2.15−18 Extensive studies into the absorption of other acidic gases such as SO2 and NO by SBILs have found that irreversible absorption was observed in many cases, often on multiple active sites within the IL, affecting the recyclability of the system.[19−25]
Summary
Post-combustion CO2 capture is an important requirement of many industrial processes. The competitive absorption of CO2 with industrially relevant concentrations of H2O, SO2, or NO, independently, has been investigated previously in [P66614][Benzim], and this IL was selected for the current study to gain a comprehensive insight into more complex, multi-component feeds.[18,26,27] The use of a recently developed analytical method utilizing mass spectrometry allows the study of this superbase IL under realistic and dry flue gas conditions, with a feed containing 14% CO2 and 0.2% NO2.26 Further molecular-level information was provided by density functional theory (DFT). The gas absorption measurement techniques used in this work were reported in detail previously, and the same protocol was followed in this work.[26,27] To briefly summarize this, the uptake of a single component gas feed (1% NO2 in argon) by [P66614][Benzim] was studied gravimetrically at 22 ± 0.5 °C.
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