Toward the Mechanism Study of Pd/γ-Al₂O₃-Assisted Bioalcohol Combustion in a Flow Reactor

Abstract

The combustion and catalytic combustion of ethanol (a typical bioalcohol) at atmospheric pressure and an equivalence ratio of ϕ = 3 were investigated in a flow reactor. Reactants, important intermediates, and products were detected and identified by gas chromatography−mass spectrometry. For ethanol combustion, the hydrogen abstraction reaction attacked by OH radicals is the initial pathway for ethanol consumption. Acetaldehyde is regarded as an important intermediate in ethanol combustion through kinetic analysis. However, catalytic combustion of ethanol over γ-Al 2 O 3 is dominated by bimolecular and unimolecular dehydration reactions to produce diethyl ether and C 2 H 4 , while Pd/γ-Al 2 O 3 can strongly oxidize ethanol to CO 2 with a dramatic decrease in the decomposition temperature. To further understand the mechanism of catalytic combustion, pyrolysis and catalytic pyrolysis of ethanol were also explored. The product distribution in catalytic pyrolysis demonstrated weaker coke deposition over γ-Al 2 O 3 in comparison to catalytic combustion. In addition, the deactivation of Pd/γ-Al 2 O 3 at high temperatures was probably due to the increase in the concentration of oxygenated species to cover the active Pd site. The apparent activation energy was estimated by the Arrhenius equation to illustrate the difference in primary reaction channels. This work bridges the gap between combustion and catalytic combustion of ethanol, which is beneficial for the improvement of catalytic performance and control of pollutants by combining pyrolysis and combustion.

Catalytic Combustion Study of Ethanol Over Manganese Oxides with Different Morphologies

“…Differently, the inner and outer diameters of the quartz reactor are 6 and 8 mm along with a length of 350 mm. According to the previous literature, a constant temperature zone of 100 mm exists in the center of the flow reactor. The catalyst was located in the middle position and had a bed depth of approximately 5 mm.…”

“…1 However, the future energy structure will be dominated by sustainable and clean fuels, with the energy shortage and the increasing environmental pollution caused by the burning of fossil fuels. 2,3 Particularly, key steps involving the growing share of nonfossil energy sources need to be carried out to achieve the carbon peak and neutrality goals of China. 4,5 As one of the alternatives, biofuel from the sustainable feedbacks has been recognized as the effective surrogate fuel applied for the gasoline engine.…”

“…The consumption and use of energy are closely associated with human society, and fossil fuels have been the dominant source of global energy . However, the future energy structure will be dominated by sustainable and clean fuels, with the energy shortage and the increasing environmental pollution caused by the burning of fossil fuels. , Particularly, key steps involving the growing share of nonfossil energy sources need to be carried out to achieve the carbon peak and neutrality goals of China. , As one of the alternatives, biofuel from the sustainable feedbacks has been recognized as the effective surrogate fuel applied for the gasoline engine. , Ethanol, the first generation biofuel, is widely employed as the additive or even alternative fuel for vehicles based on the following advantages: (1) high octane number; (2) abundant production sources and mature technology; (3) high oxygen content of 34.8%. Most notably, the addition of ethanol in the combustion process can effectively reduce soot emissions and make the combustion more thorough. − However, the harmful byproduct (i.e., acetaldehyde) from the incomplete combustion of ethanol is considered to be responsible for the formation of photochemical smog .…”

Zero-Carbon and Carbon-Neutral Fuels: A Review of Combustion Products and Cytotoxicity

“…Moreover, there are other conventional contaminants: NOx and HC, such as methane (CH 4 ), ethane (C 2 H 4 ), and acetylene (C 2 H 2 ) [62]. The unconventional pollutants produced by the combustion of alcohol fuels mainly include aldehydes, ketones, acids, unburned alcohols, enols, and olefins [63][64][65][66][67][68][69][70][71][72][73][74]. Alcohols do not contain unsaturated bonds such as C=C, so their combustion does not produce soot [75].…”

Comparative Study of the Catalytic Oxidation of Hydrocarbons on Platinum and Palladium Wires and Nanoparticles

“…Most reported studies of catalytic oxidation employ supported Pt and Pd, − where the support is mainly a more accessible metal oxide such as aluminum oxide, − cerium oxide, , and silicon dioxide , or metal such as nickel, barium, zeolite, and zirconium. , While such configurations are relevant for practical applications, they come with the complexity of the role played by the support and uncertainty of mechanisms explaining the interchanging reactions between noble metals, support, and gaseous reactants. Only a handful of papers are reported for pure unsupported noble metals reacting with a limited range of hydrocarbon fuels .…”