The Effect of Citric Acid Concentration on the Properties of LaMnO3 as a Catalyst for Hydrocarbon Oxidation

Abstract

LaMnO3 (LM) catalysts with a molar ratio of citric acid (CA) to metal (La3+ + Mn2+) nitrates ranging from 0.5 to 2 (LM0.5 to LM2) were synthesized by the citrate sol–gel method with the aim of studying the effect of the citric acid ratio on the physicochemical properties and the catalytic performance in hydrocarbon oxidation. Structural and morphological properties of these catalysts were characterized by X-ray diffraction (XRD) and specific surface area (N2 adsorption) measurements, while the chemical composition was determined by inductively coupled plasma atomic emission spectroscopy (ICP-OES). In the selected samples, additional characterizations were carried out by thermogravimetric and differential thermal analysis (TGA/DTA), Fourier Transform Infrared Spectroscopy (FT-IR), temperature-programmed reduction by hydrogen (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The results showed that the amount of citric acid used significantly influenced the TGA/DTA profile of gels along with the physicochemical properties of the catalysts. The XRD patterns are consistent with the perovskite formation as the main phase. The segregation of a small amount of Mn3O4, detected for molar ratios ranging between 0.5 and 1.5, suggested the formation of a slightly nonstoichiometric LaMn1−xO3 phase with a relatively high content of Mn4+. The catalytic performance was evaluated in the total oxidation of two selected hydrocarbons, toluene and propene, which represent typical volatile organic compounds (VOCs). Typically, three consecutive catalytic cycles were performed in order to reach steady-state performance in toluene and propene oxidation. Moreover, the stability of the catalysts under reaction conditions was investigated through 24-h experiments at 17% of toluene conversion. The catalysts LM1.2, LM1.3, and LM1.5 showed the best catalytic performance in both hydrocarbon oxidations, well comparing with the Pd/Al2O3 used as a reference.

Sucrose-Assisted Solution Combustion Synthesis of Doped Strontium Ferrate Perovskite-Type Electrocatalysts: Primary Role of the Secondary Fuel

“…For example, Aliotta et al [7], regarding the SCS of Ce 0.8 Sm 0.2 O 2 , hypothesized that sucrose is able to form a gel network where metal cations remain trapped in sucrose-metal cation agglomerates, with a positive effect on the porosity, grain growth, and densification of the powders. This specific template function of sucrose has been reported as well by other authors, highlighting that, by using sucrose as a fuel, high surface area powders with low agglomeration degrees are produced [7,8,[10][11][12][13]. Sucrose is often used to create a reducing environment around a metal cation and govern oxidation states [14].…”

Promoting Effect of Palladium on ZnAl2O4-Supported Catalysts Based on Cobalt or Copper Oxide on the Activity for the Total Propene Oxidation

“…It is important to point out that the materials studied in this work, and particularly the PdCo-ZnAl catalyst, presented high activity, comparable to those reported in the literature [8,[65][66][67][68][69][70][71][72][73][74][75][76]. For comparative purposes, a selection of reported catalytic results, in terms of the required temperature to obtain 50% of propene oxidation, is presented in Table 5.…”

Effect of the Preparation Method of LaSrCoFeOx Perovskites on the Activity of N2O Decomposition

“…Initially, two Sr x Co y M z -based perovskite materials (where M = La or Fe) were prepared by a sol-gel method with citric acid, as previously reported [43,[49][50][51][52][53][54][55]. La 0.75 Sr 0.25 CoO x (denoted LSC) and SrCo 0.81 Fe 0.19 O x (denoted SCF) were prepared by the combination of citric acid and metal nitrates using a molar ratio of 2:1.…”