Reduction and Aromatization Activity of MoO3/Al2O3 Catalysts: The Identification of The Active Mo Oxidation State on the Basis of Reinterpreted Mo 3d XPS Spectra

Molecular Structure–Reactivity Relationships for Olefin Metathesis by Al2O3-Supported Surface MoOx Sites

“…The molecular structures of the alumina-supported MoO x sites depicted in Scheme 1 are in agreement with the structures proposed from previous characterization studies of dehydrated supported MoO x /Al 2 O 3 catalysts: in situ XANES, 8,9 in situ Raman, 8,9 in situ UV−vis, 7 and XPS. 14 The surface MoO x sites preferentially anchor to the alumina support at more basic HO-μ 1 -Al IV surface hydroxyls at low surface molybdena coverage and to some of the more acidic HO-μ 1/3 -Al V/VI surface hydroxyls. At high surface molybdena coverage, all of the alumina HO- While the oligomeric surface MoO x sites readily form oxygenates at lower temperatures (∼25−200 °C), the isolated surface MoO x sites only form oxygenates at higher temperatures (>400 °C).…”

“…10 In the earliest characterization studies of activated MoO x surface sites on Al 2 O 3 , the MoO x had been exposed to propylene metathesis reaction conditions and subsequently exposed to ambient conditions and examined with ex situ XPS and EPR spectroscopy. 14,15 These studies detected both Mo 6+ and Mo 4+ oxidation states, and it was suggested that other Mo oxidation states are not active for olefin metathesis. From ex situ solid-state 27 Al NMR of mesoporous Al 2 O 3 -supported MoO x catalysts, 16 it was proposed that surface MoO x sites anchored to AlO 6 sites are the most active sites.…”

Investigation of MoOx/Al2O3 under Cyclic Operation for Oxidative and Non-Oxidative Dehydrogenation of Propane

“…Excluding these first 10 min of the second ODP run which can be attributed to coke combustion, the amount of CO 2 formed in both ODP runs was approximately equal, no CO 2 is detected under DP. Despite significant differences in propene formation in the first and second ODP runs, similar CO 2 formation indicated the occurrence of competitive reactions (other than combustion) such as aromatization, which is known for Mo oxide based catalysts [11,15,[18][19][20][21]. Such side reactions might have dominated in the first ODP run while they appeared to have been suppressed in the second ODP.…”

“…It is widely accepted that the nature and distribution of Mo oxide species depend sensitively on several parameters such as Mo loading, catalyst support and calcination procedure, resulting in a variety of species spanning from monomeric, dimeric and oligomeric Mo oxide species to large Mo oxide clusters [8,11,[15][16][17]. The surface composition of the catalyst determines the catalytic properties in various petro-and fine-chemical processes such as oxidation, metathesis, aromatisation and dehydrogenation of lower alkanes [15,[18][19][20][21][22][23][24]. For example, by in situ Raman studies on MoO x /Al 2 O 3 it is suggested that oligomeric Mo oxide species are more active for propene metathesis than monomeric species or large clusters [15], while oxidative dehydrogenation of ethane (ODE) activity is related to monomeric Mo-O-Al species [17].…”

Zeolite Stabilized Isolated Molybdenum Species for Catalytic Oxidative Desulfurization

“…负载型氧化钼催化剂, 即将氧化钼负载在不同的载 体上, 在一系列重要反应中表现出显著的催化活性, 在 过去的几十年中得以深入研究. 例如: 烯烃复分解 [25][26][27][28][29][30][31][32][33][34][35] , 轻烷烃氧化脱氢 [36][37][38][39][40][41][42] , 含氧化合物选择性氧化 [43][44][45][46][47] 和甲 烷脱氢芳构化 [48][49][50][51][52][53] 等. 众所周知, 负载型氧化钼催化剂 在各种反应中的催化活性取决于钼氧物种的分子结构.…”