Rate Inhibition and Enhancement on Ceria-Promoted Pd Monolith Catalysts: Oxidation of Acetylene, Ethylene, and Propylene and Their Mixtures

Abstract

The catalytic oxidations of acetylene, ethylene, and propylene under transient and steady-state conditions were studied using model Pd/Al2O3 and Pd/CeO2–ZrO2 monolith catalysts. Kinetics and light-off measurements highlight the differences between the oxidation of each hydrocarbon. Acetylene is strongly self-inhibiting and −1 order while the reaction order with respect to ethylene is +1, both at temperatures below light-off. Ethylene oxidation is moderately inhibited by oxygen at low temperatures and ethylene at high temperatures. Mixture light-off experiments reveal acetylene inhibits the oxidations of ethylene, propylene, and CO. Light-off of the other species follow acetylene oxidation, which is nearly unaffected by the other species. The Pd/CeO2–ZrO2 catalyst gives consistently higher conversion compared with Pd/Al2O3 at the same Pd loading for each of the individual oxidation reactions, although the negative-order kinetics of acetylene is sustained. Oxidation of acetylene and mixtures containing acetylene are enhanced with Pd/CeO2–ZrO2 compared to Pd/Al2O3. The effects of oxidative or reductive pretreatment of the catalysts on species oxidations are also evaluated. Mechanistic implications for the reactions are described to guide kinetic model development. The findings highlight and clarify inhibition effects during single and co-oxidation and offer insights into optimizing the catalyst composition and its operation.

Nanostructured Equimolar Ceria-Praseodymia for Total Oxidations in Low-O2 Conditions

“…abatement of these compounds is of high importance due to the fact that some of them are toxic for human health [42][43][44] and they can also foster the photochemical generation of secondary pollutants, such as ozone [45]. Since ceria-based oxides can be used as catalysts [46][47][48] or noble metals supports [29,49,50] for VOCs' oxidation, CeO2 and Ce50Pr50 are expected to affect these kinds of reactions. The catalytic tests were carried out at two different concentrations of oxygen, in order to evaluate the effect of this parameter.…”

Yttrium stabilization and Pt addition to Pd/ZrO2 catalyst for the oxidation of methane in the presence of ethylene and water

“…[11][12][13][14] Nevertheless, the inuence of Pt on the improvement of bimetallic Pd-Pt catalysts is inconclusive. Though some literature state that alloying Pt to Pd increases catalytic activities, 8,12,15,16 others argue that the impact of adding Pt to Pd is not obvious. 14,17,18 Persson et al compared the catalytic activity of Pd and bimetallic Pt-Pd catalysts and found that the addition of Pt to Pd has detrimental effects and it even lowers the performance of the monometallic Pd catalyst.…”

“…17 However, notably, the addition of Pt has promotional effects on the dispersion of supported Pd catalysts. 8 Among other factors, support materials have an important inuence on the catalytic properties. The inuence of the support originates from its interaction with the depositing metal species.…”

“…Similar to methane, ethylene can be converted to carbon dioxide over a catalyst. 8 C 2 H 4 + 3O 2 → 2CO 2 + 2H 2 O; Δ H r = −1322 kJ mol −1 . …”

“… 17 However, notably, the addition of Pt has promotional effects on the dispersion of supported Pd catalysts. 8 …”