Transient in‐situ DRIFTS Investigation of Catalytic Oxidation of Toluene over α‐, γ‐ and β‐MnO₂

Abstract

Manganese oxides with different crystal phases (i. e. α‐MnO2, γ‐MnO2 and β‐MnO2) were synthesized for catalytic oxidation of toluene. The catalytic activity was strongly influenced by the crystal phases of MnO2. α‐MnO2 exhibited the highest catalytic activity with a 50 % toluene conversion (T50) at 229 °C and a 90 % toluene conversion (T90) at 238 °C, followed by γ‐MnO2 (T90=252 °C) and β‐MnO2 (T90=278 °C). The remarkable catalytic activity of α‐MnO2 was attributed to its superior redox property and lattice oxygen mobility. Different intermediates were detected on the surfaces of α‐, γ‐ and β‐MnO2 by in situ diffuse reflectance infrared Fourier transform spectroscopy (in‐situ DRIFTS). Benzoate species were found to be the key intermediates on α‐MnO2 at 240 °C, while benzoyl oxide species and benzoate were the major intermediates on γ‐MnO2 at 260 °C. The surface of β‐MnO2 was mainly covered by carbonate and benzoate species after the adsorption of toluene at 280 °C.

Recent Progress of Thermocatalytic and Photo/Thermocatalytic Oxidation for VOCs Purification over Manganese-based Oxide Catalysts

“…As a promising catalyst, MnO 2 exists in various crystal forms (such as α, β, γ, δ, and ε), in which they have different tunnel sizes, surface active oxygen, and redox capacity, leading to the differences in the catalytic activity of VOCs. 22,33,34 Four different crystal forms (α, β, γ, and δ) of MnO 2 were synthesized through hydrothermal method. 27 The [2 × 2] 1D tunnel on α-MnO 2 , [1 × 1] 1D tunnel on β-MnO 2 , an intergrowth of [1 × 1] and [1 × 2] 1D tunnel on γ-MnO 2 and 2D layered structure with K + and H 2 O within its interlayer on δ-MnO 2 were presented in Figure 1a.…”

“…20,21 Among them, manganese-based (Mn-based) oxides, as economical and practical environmentally friendly materials, are one of the most competitive and promising candidates for the catalytic degradation of VOCs both in thermocatalytic or photo/thermocatalytic systems. 22 In the past decade, various Mn-based oxides have been prepared via different strategies to optimize their catalytic performances and study catalytic behaviors in the oxidation of VOCs. To date, catalytic removal of toluene over Mn-based oxide catalysts have been reviewed.…”

“…Commonly, according to active ingredients, catalysts used for VOCs degradation are divided into two categories: noble metal-based catalysts and non-noble metal oxide catalysts. The former usually display preferable catalytic performance, but they are expensive and easily inactive. − Non-noble metal oxide catalysts, including oxides of Cu, Mn, Co, Fe, etc., although the activity maybe not as good as that of noble metal catalysts, their inexpensiveness and long-term thermal stability have drawn increasing attention and have the potential to be dominant in the future. , Among them, manganese-based (Mn-based) oxides, as economical and practical environmentally friendly materials, are one of the most competitive and promising candidates for the catalytic degradation of VOCs both in thermocatalytic or photo/thermocatalytic systems …”

TiO2@UiO‐66 Composites with Efficient Adsorption and Photocatalytic Oxidation of VOCs: Investigation of Synergistic Effects and Reaction Mechanism

“…Volatile organic compounds (VOCs) are considered as a kind of toxic pollutants in the atmosphere, which are mainly from building materials, furniture, decoration materials and other consumer products [1,2] . They not only give rise to a harmful effect on human health but also lead to serious ecosystem effects [3,4] . Semiconductor photocatalysis has been proved to be an effective and promising alternative technology for the removal of VOCs from the atmospheric environment under mild operating conditions [5–7] …”

A MnOx enhanced atomically dispersed iron–nitrogen–carbon catalyst for the oxygen reduction reaction

“…As shown in Fig. 3a, the Mn 2p 3/2 spectrum of the Mn-Fe-N-C SAC can be split into three bands with energy peaks at 639.5, 641.1, and 643.2 eV, which are ascribed to Mn 2+ , Mn 3+ , and Mn 4+ species based on bonding energies, 33,34 respectively, revealing the co-existence of three kinds of Mn species on the surface of the Mn-Fe-N-C SAC. The ratio of (Mn 2+ + Mn 3+ )/Mn total based on the XPS peak areas is 0.53, implying that abundant oxygen vacancies exist in MnO x .…”