LaCl3-based catalysts for oxidative chlorination of CH4

Abstract

LaCl 3 is an active, selective and stable catalyst for oxidative chlorination of methane to methyl chloride. Selective conversion to methyl chloride can be achieved by limiting methane conversion, for example, by using an excess of methane in the feed. Methylene chloride and carbon monoxide are the main side products at higher methane conversion levels. Transient OCl ) anion, formed by oxidation of Cl ) in LaOCl and LaCl 3 with molecular oxygen, is proposed to be the active site for the initial step of methane activation. CO x formation is proposed to proceed through the formation of adsorbed multiply substituted chloromethanes.

Modified Lanthanum Catalysts for Oxidative Chlorination of Methane

“…It is important to note that the selectivity to methyl chloride is lower and the initial oxidation of methane to CO is higher than in the material reported in [7,8] We speculate at present that the materials prepared here, retain a part of the formed methyl chloride species on their surface. This leads to a catalytic pathway that favors the reaction of the (partially chlorinated) methyl species with the hydroxy groups formed during the initial steps or with oxygen present in the sample.…”

“…in an OCl -anion as shown by DFT calculations [7]. Under steady state conditions, the adsorption of oxygen can, therefore, not cause the formation of stable OCl -, but transient species could cause a synproportionation of Cland Cl ?…”

“…Recent reports [7,8] showed that LaCl 3 is a promising stable catalyst for the conversion of methane to methyl chloride by oxidative chlorination using oxygen and HCl. It is superior to the well-established copper based catalysts [9][10][11][12], which are unstable and volatile under reaction conditions.…”

“…The latter also catalyze the formation of chlorine via the Deacon reaction, initiating radical gas phase chlorination with low selectivity towards methyl chloride. LaCl 3 catalyzes the reaction without a change in the oxidation state of lanthanum through a surface catalyzed reaction with a transient hypochlorite species as active site [7]. The hypochlorite species is formed on the chloride surface by reaction with oxygen from the gas phase.…”

Structure and phase analysis of one-pot hydrothermally synthesized FePO4-SBA-15 as an extremely stable catalyst for harsh oxy-bromination of methane

“…However, halogens are highly corrosive to equipment and dangerous to handle which present a big trouble for the industrialization. In view of halogen corrosion, methane oxidative bromination [5][6][7][8] and chlorination [9] were studied which use hydrobromic acid or HCl as reactants instead of halogens to reduce corrosion problem. Zhou et al [5,6,10] firstly reported methane oxidative bromination (OBM) reaction and developed Ru-and Rh-containing catalysts which showed high selectivity for CH 3 Br and excellent stability, but the uses of noble metals raise the production cost.…”