Low‐Temperature Destruction of Carbon Tetrachloride over Lanthanide Oxide‐Based Catalysts: From Destructive Adsorption to a Catalytic Reaction Cycle

Abstract

The catalytic destruction of carbon tetrachloride in the presence of steam, CCl4 + 2 H2O→4 HCl + CO2, was investigated at 200–350 °C over a series of lanthanide (La, Ce, Pr and Nd) and alkaline‐earth metal (Mg, Ca, Sr and Ba) oxide‐based catalysts with kinetic experiments, Raman spectroscopy, X‐ray photoelectron spectroscopy, IR spectroscopy, X‐ray diffraction, and DFT calculations. This new catalytic reaction was achieved by combining destructive adsorption of CCl4 on a basic oxide surface and concurrent dechlorination of the resulting partially chlorinated solid by steam. The combination of the two noncatalytic reactions into a catalytic cycle provided a rare opportunity in heterogeneous catalysis for studying the nature and extent of surface participation in the overall reaction chemistry. The reaction is proposed to proceed over a terminal lattice oxygen site with stepwise donation of chlorine atoms from the hydrocarbon to the surface and formation of the gas‐phase intermediate COCl2, which is readily readsorbed at the catalyst surface to form CO2. In a second step, the active catalyst surface is regenerated by steam with formation of gas‐phase HCl. Depending on the reaction conditions, the catalytic material was found to transform dynamically from the metal oxide state to the metal oxide chloride or metal chloride state due to the bulk diffusion of oxygen and chlorine atoms. A catalyst obtained from a 10 wt % La2O3/Al2O3 precursor exhibited the highest destruction rate: 0.289 g CCl4 h−1 g−1 catalyst at 350 °C, which is higher than that of any other reported catalyst system.

Enhancement of the low temperature chlorination of ilmenite with CCl4 by adding Cl2

“…Mechanism of chlorination. [8,15,31], the subsequent reactions of Fe 3+ and Ti 4+ in the intermediate phases can be written as Eqs. (3) and (4) O ] IP + CCl 4 (g) → 2TiCl 4 (g) + CO 2 (g) (4) The reaction mechanism is shown in Fig.…”

“…CCl 4 is an ozone depleting substance and may not to be released into the atmosphere by the Montreal Protocol. It is an unavoidable byproduct in the production of the chlorides of methane (CHCl 3 and CH 2 Cl 2 ), thus, there has been much fundamental and applied research on its removal by its destructive adsorption on metal oxides [7][8][9][10][11][12][13][14][15]. A better choice is converting CCl 4 to valuable products [16][17][18], such as TiCl 4 .…”

Dehydrochlorination of Intermediates in the Production of Vinyl Chloride over Lanthanum Oxide-Based Catalysts

“…Even though the peaks are much broader in the amorphous LaOCl catalyst material, the similarity is straightforward. [29][30][31][32][33]. This is caused by the solid-state diffusion of oxygen and chlorine atoms between the catalytic surface and the bulk.…”

“…Even though transition metal oxides are very active for the dechlorination of CHCs, the chlorination of the oxide may result in the formation of toxic volatile transition metal oxychlorides [14][15][16][17][18][19][20][21]. The basic oxides have proven to be stable active materials for the conversion of CHCs [22][23][24][25][26][27][28][29][30][31][32][33][34]. In previous work, lanthanum oxide-based catalysts were found to have the highest destructive capacity for the catalytic destruction of chlorinated C 1 and have been studied in detail in our group [29-31, 33, 34].…”

Eco-efficient Catalytic Hydrodechlorination of Carbon Tetrachloride in Aqueous Cyclodextrin Solutions

“…Thermal combustion in gas phase is based on the total oxidation at high temperatures generally above 800°C of the molecules in the ultimate products such as carbon dioxide, water, and hydrochloric gas [5]. Furthermore, the addition of an oxidation catalyst enables the reaction to occur at lower temperatures than those required by conventional thermal oxidation [6,7]. Nevertheless, oxidation processes (thermal or catalytic) remain energetically expensive and require the installation of special reactors that should be resistant against the corrosive gas emissions.…”