On the role of heterogeneous and homogeneous processes in oxidative dehydrogenation of C3-C4 alkanes

Alkane Activation at Ambient Temperatures: Unusual Selectivities, CC, CH Bond Scission versus CC Bond Coupling

“…Most remarkably, very high selectivity to ! C 4 components was observed (C 4 is 13 %, C 4 + is 24 %). In order to highlight this, typical product distribution obtained in an empty quartz tube reactor (internal diameter 4 mm) operating at 600C (same feed composition) [29] is given in Figure 3 and compared with the results discussed above.…”

“…For example, oxidative methane conversion requires temperatures in the range of 850 8C, for ethane 750 8C and even for liquid petroleum gas (LPG) range hydrocarbons (C 3 + C 4 ) temperatures above 600 8C are required. [4] Activation of CÀC and CÀH bonds at higher temperatures, even in the presence of heterogeneous catalyst systems, tend to be initiated by homogeneous splitting of the bond, creation of radicals and radical chain reactions leading to products. [5][6][7] High-temperature alkane conversions have inherent difficulties, namely that 1) they lead to extensive endothermic CÀC and CÀH bond cleavage causing formation of cracking products or coke, respectively, 2) cause loss of catalyst activity due to sintering and 3) favor non-selective combustion of alkanes.…”

Heterogeneous–homogeneous interactions in catalytic microchannel reactors

“…Margolis and coworkers were among the first to establish their role in catalytic oxidation of hydrocarbons 1 and, since then, a large number of investigations have established the importance of coupled heterogeneoushomogeneous reactions in a wide variety of reactions systems, most notably in catalytic combustion, [2][3][4] partial oxidation of small alkanes, [5][6][7] and oxidative coupling of methane. 8,9 All of these reactions systems have very high reaction temperatures (T Ͼ 700°C) as a common characteristic.…”

Heterogeneous Partial (amm)Oxidation and Oxidative Dehydrogenation Catalysis on Mixed Metal Oxides

“…The process starts with the abstraction of a proton in α of the double bond by surface O 2´a nd the sharing of electron between C=C and the empty d˝orbital, by a two-electron transfer that reduces the transition metal cations. Reaction mechanisms in partial oxidation reactions may also include homogeneous phase reaction (radical-type mechanism), in addition to the usual heterogeneous one, even at relatively low temperatures such as below 300˝C while it occurs usually at high temperatures (600˝C and above) [17].…”