Wenlin Li,Feng Li,Junwen Chen,Luis E. Betancourt,Chunyan Tu,Mingjie Liao,Xing Ning,Jiajun Zheng,Ruifeng Li
The hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) is an essential reaction step to produce value-added renewable chemicals and fuels. In this study, it is demonstrated that the dispersed state of metal and the acid properties of the support can be tuned directly in the synthesized stage for the Ru/MCM-49 catalysts. The average metal particle size of Ru was found at ∼2.0 nm, and strong metal–support interaction was observed for the Ru/MCM-49(DP) catalyst. Mesopores presented can enhance the conversion rate for LA to GVL. The presence of a higher amount of Lewis acid sites can promote the ring closure esterification of the intermediate 4-HPA. High catalytic activity with a TOF value of >3000 h–1, as well as excellent reusability, were achieved by Ru/MCM-49(DP). The agglomeration of Ru particles and the coke formation were thought to be responsible for the deactivation of the catalyst.
Graphical Schematic diagram of the dominant mechanism of NH 3 -SCR reaction on CeCu/MCM-49 catalyst before and after poisoning. The L−H mechanism was dominant before poisoning. However, after alkali metal poisoning, NO x adsorption on the catalyst is inhibited, so the E−R mechanism dominates. NO x is a common atmospheric pollutant, and NH 3 -SCR technology efficiently purifies it. CeCuO x binary-oxide nanoparticles were synthesized and loaded onto acid MCM-49 molecular sieve with a large specific surface area to increase acid sites and disperse active sites of the catalyst. The optimized 35 % CeCu/MCM-49 catalyst effectively purified over 80 % of NO x in the temperature range of 200–500 °C and demonstrated excellent resistance to alkali metals, such as K, Na, and Ca. Even after K poisoning, it still removed over 80 % of NO x in the range of 200–450 °C. Various characterization methods, including XRD, FT-IR, TEM, and N 2 isotherm adsorption-desorption tests, confirmed the structure of the catalyst remained intact after poisoning with no substance change, nor agglomeration of nanoparticles. NH 3 -TPD and H 2 -TPR confirmed that the catalyst had effective acidity and redox capacity that were not affected by alkali metals. In-situ DRIFTs showed that the catalytic reaction predominant mechanism shifted from L−H to E−R mechanism after poisoning. This study provides valuable insights into the development of high-performance Ce-based NH 3 -SCR catalysts with alkali metal resistance.
Shiyong Xing,Yan Cui,Tiefeng Wang,Jinwei He,Minghan Han
In the present work, the effect of oxides on the alkylation of benzene with 1-dodecene was comprehensively investigated over MCM-49 n -heptanol, n -heptaldehyde and n -heptanoic acid were selected as the model oxides herein, and obvious decrease of lifetime could be caused by only trace amount of oxides added in the feedstocks. However, the deactivated catalysts were difficult to be regenerated by extraction with hot benzene. Additionally, coke-burning was also proved to be incapable to regenerate the deactivated catalysts mainly for the dealumination during calcination . Further characterizations complementary with DFT calculations were conducted to demonstrate that the deactivation was mainly due to the firm adsorption of oxides on the acid sites.
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