On the Activity and Selectivity of CoAl and CoAlCe Mixed Oxides in Formaldehyde Production from Pulp Mill Emissions

Abstract

Contaminated methanol has very good potential for being utilized in formaldehyde production instead of its destructive abatement. The activities, selectivities and stabilities of cobalt–alumina and cobalt–alumina–ceria catalysts prepared by the hydrotalcite-method were investigated in formaldehyde production from emissions of methanol and methanethiol. Catalysts were thoroughly characterized and the relationships between the characterization results and the catalytic performances were drawn. The preparation method used led to the formation of spinel-type structures in the form of Co2AlO4 based on x-ray diffraction (XRD) and Raman spectroscopy. Ceria seems to be present as CeO2, even though interaction with alumina is possible in the fresh catalyst. The same structure is maintained after pelletizing the cobalt–alumina–ceria catalyst. The cobalt–alumina–ceria catalyst was slightly better in formaldehyde production, probably due to lower redox temperatures and higher amounts of acidity and basicity. Methanol conversion is negatively affected by the presence of methanethiol; however, formaldehyde yields are improved. The stability of the pelletized catalyst was promising based on a 16 h experiment. During the experiment, cobalt was oxidized (Co2+ → Co3+), cerium was reduced (Ce4+ → Ce3+) and sulfates were formed, especially on the outer surface of the pellet. These changes affected the low temperature performance of the catalyst; however, the formaldehyde yield was unchanged.

Vanadia–Zirconia and Vanadia–Hafnia Catalysts for Utilization of Volatile Organic Compound Emissions

“…DMDS and DMS can be further reacted according to the Equations (7)–(10) [ 4 , 32 ]: H 3 SSCH 3 + O 2 -> 2HCHO + 2SO 2 + H 2 O CH 3 SCH 3 + 2 ½ O 2 -> 2HCHO + SO 2 + H 2 O CH 3 SSCH 3 + 5 ½ O 2 -> 2CO 2 + 2SO 2 + 3H 2 O CH 3 SCH 3 + 4 ½ O 2 -> 2CO 2 + SO 2 + 3H 2 O …”

“…DMDS and DMS can be further reacted according to the Equations ( 7)-( 10) [4,32]: The results of the experiments realized with VZr and VHf catalysts (Figure 5) show that methanethiol reaction starts at a lower temperature range than that of methanol. This is due to the lower total dissociation energy and longer C-S bond of methanethiol compared with the bonds of methanol molecule [5,33].…”

“…Earlier studies have demonstrated the activity of cobalt–alumina and cobalt–alumina-ceria catalysts [ 4 ], as well as vanadia supported on silica and titania [ 5 ] in formaldehyde production from contaminated methanol. Our earlier study has also demonstrated better performance of ZrO 2 and HfO 2 compared to Al 2 O 3 support in the case of vanadia catalysts [ 6 ].…”

Reducibility of Al3+-Modified Co3O4: Influence of Aluminum Distribution

“…Thus, the lower mobility of the Al 2 O 3 modifier, caused by its interaction with cobalt particles on the surfaces of the mesoporous Co 3 O 4 , improved the FTS activity and stability, with less coke or wax deposition on the active sites [ 34 ]. In some cases, interaction led to the full dissolution of Al 3+ ions in Co 3 O 4 , along with the formation of (Co,Al) 3 O 4 solid solutions, which in turn demonstrate catalytic properties in methane decomposition [ 35 ], OER [ 36 ], toluene total oxidation [ 37 ], and formaldehyde production from emissions of methanol and methanethiol [ 38 ]. The substitution of Co 2+ and Co 3+ ions by Al 3+ ions modulates the catalysts’ surface morphology towards a more electrocatalytically active one and tailors the energy level for faster charge transfer in (Co,Al) 3 O 4 samples, which are highly efficient electrocatalysts for water oxidation [ 36 ].…”