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Identifying the Catalytic Active Site for Propylene Metathesis by Supported ReOx Catalysts
ACS Catalysis ( IF 12.9 ) Pub Date : 2021-01-31 , DOI: 10.1021/acscatal.0c04773
Bin Zhang 1 , Israel E. Wachs 1
Affiliation  

A series of supported ReOx catalysts were investigated that allowed identifying the unique surface anchoring sites on oxide supports responsible for activating the surface ReO4 sites for propylene metathesis (the catalytic active site). The catalysts were synthesized by incipient-wetness impregnation of aqueous HReO4 onto the oxide supports (Al2O3, ZrO2, TiO2, SiO2, and CeO2), characterized under dehydrated and propylene metathesis reaction conditions with in situ spectroscopy (Raman, DRIFTS, UV–vis and NAP-XPS), and chemically probed (CH3CH═CH2–TPSR, CH2═CH2/CH3CH═CHCH3 titration and steady-state self-metathesis of propylene to ethylene and 2-butene). The initially calcined supported rhenia species anchor as isolated surface Re7+O4 sites on the oxide supports by reacting with the surface hydroxyls (terminal S–OH, bridged S–OH–S, and tricoordinated S3–OH) of the oxide supports. The specific oxide support was found to control the number of activated sites (Al2O3 ≫ ZrO2 > CeO2 > TiO2 > SiO2) and propylene metathesis activity (Al2O3 ≫ ZrO2 ≫ TiO2 ∼ CeO2 ∼ SiO2), revealing that the oxide support action is a potent ligand for the surface ReOx sites. The activation and specific activity of the surface ReOx sites depend on several factors (nature of surface hydroxyls (S3–OH > S–OH–S > S–OH), coordination of the oxide support surface cation (ZrO7, AlO6, CeO4) and electronegativity of the oxide support cation (SiO2 > Al2O3 > TiO2 > ZrO2 > CeO2). No relationships exist between olefin metathesis activity and acid strength of surface Lewis and Brønsted sites. Prior studies primarily focused on supported ReOx/Al2O3, and the lack of examination of non-Al2O3 supported rhenia catalysts precluded comparison between efficient and inefficient olefin metathesis catalysts, which prevented identifying the catalytic active site for olefin metathesis by supported ReOx catalysts.

中文翻译:

通过支持的ReO x催化剂鉴定丙烯复分解的催化活性位

研究了一系列负载的ReO x催化剂,这些催化剂可以识别氧化物载体上独特的表面锚固位点,该位点负责活化丙烯复分解的表面ReO 4位(催化活性位)。通过在水溶液和丙烯复分解反应条件下用原位光谱法对HReO 4水溶液进行湿润浸渍浸渍到氧化物载体(Al 2 O 3,ZrO 2,TiO 2,SiO 2和CeO 2)上进行合成。拉曼,DRIFTS,UV-vis和NAP-XPS),和化学探测(CH 3 CH = CH 2 -TPSR,CH2 = CH 2 / CH 3 CH = CHCH 3滴定和丙烯的稳态自复分解,以乙烯和2-丁烯)。通过与氧化物载体的表面羟基(末端S–OH,桥连的S–OH–S和三配位S 3 –OH)反应,最初煅烧的负载型rh属物种在氧化物载体上作为孤立的表面Re 7+ O 4位点锚定。具体氧化物载体被发现控制活化位点的数量(铝2 ö 3 »的ZrO 2 >的CeO 2 >的TiO 2 >的SiO 2)和丙烯复分解活性(的Al 2 ö3 »的ZrO 2 »的TiO 2〜的CeO 2〜的SiO 2),揭示了氧化物载体作用是用于表面REO一种强效配体X的网站。表面ReO x位点的活化和比活取决于几个因素(表面羟基的性质(S 3 -OH> S-OH-S> S-OH),氧化物支持表面阳离子的配位(ZrO 7,AlO 6),CeO 4)和氧化物负载阳离子的电负性(SiO 2 > Al 2 O 3 > TiO 2 > ZrO 2 > CeO 2)。烯烃的复分解活性与表面路易斯和布朗斯台德位点的酸强度之间没有关系。先前的研究主要集中在负载的ReO x / Al 2 O 3上,并且由于缺乏对非Al 2 O 3负载的en催化剂的研究,因此无法比较高效和低效率的烯烃复分解催化剂,从而无法通过以下方法确定烯烃复分解的催化活性位点负载的ReO x催化剂。
更新日期:2021-02-19
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