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This paper studies the effect of addition of Zn and ultrasound-assisted co-precipitation on Cu-Mn oxide catalysts for the oxidation of CO. Cu-Mn-Zn oxide catalysts were synthesised at different molar ratios and characterised and evaluated for CO oxidation performance. Scanning electron microscopy (SEM) imaging showed that the morphologies and textural properties of the catalysts were markedly affected by the different synthesis conditions, notably the formation of different geometries of various sizes depending on the Zn loading used. Characterisation results also revealed that both the addition of Zn and the use of ultrasound-assisted synthesis improved the dispersion of metal constituents in the mixed oxide phase, evident from the lower peak intensity and smaller crystallite sizes and more dispersed particles as seen in SEM imaging. Gas adsorption results revealed that Zn loading influences the porosity and adsorption capability of the catalyst. Zn-loaded samples exhibited a H3 hysteresis loop, which suggests the presence of slit-like pores. Temperature-programmed reduction results indicate that sonicated samples exhibit improved reduction capabilities which can increase overall catalytic activity. Results showed that Cu/Mn/Zn = 2:1:0.5 displayed the highest activity, showing 76.0% and 82.8% for CO and SO2 at 130 °C, respectively. This work has confirmed that the addition of 0.5 molar ratio of Zn and the presence of ultrasonic treatment during the catalyst synthesis have improved the overall catalytic performance, while further addition in Zn concentrations resulted in an adverse effect on the catalyst. [ABSTRACT FROM AUTHOR]

The utilisation of ultrasound in chemical preparation has been the focus of intense study in various fields, including materials science and engineering. This paper presents a novel method of synthesising the copper-manganese oxide (Hopcalite) catalyst that is used for the removal of volatile organic compounds and greenhouse gases like carbon monoxide. Several samples prepared under different conditions, with and without ultrasound, were subjected to a series of characterisation tests such as XRD, BET, FE-SEM, EDX, TPR-H 2 , TGA and FT-IR in order to establish their chemical and physical properties. A series of catalytic tests using a micro-reactor were subsequently performed on the samples in order to substantiate the aforementioned properties by analysing their ability to oxidise compressed natural gas (CNG), containing methane and sulphur dioxide. Results showed that ultrasonic irradiation of the catalyst led to observable alterations in its morphology: surfaces of the particles were noticeably smoothed and an increased in amorphicity was detected. Furthermore, ultrasonic irradiation has shown to enhance the catalytic activity of Hopcalite, achieving a higher conversion of methane relative to non-sonicated samples. Varying the ultrasonic intensity also produced appreciable effects, whereby an increase in intensity results in a higher conversion rate. The catalyst sonicated at the highest intensity of 29.7 W/cm 2 has a methane conversion rate of 13.5% at 400 °C, which was the highest among all the samples tested. [ABSTRACT FROM AUTHOR]

Spent catalysts generated from various processing industries such as those involved in the hydrogenation of fats and oils pose severe environmental issues if not treated and disposed of aptly. In this present work, process intensification was provided by the means of ultrasonic irradiation via an ultrasonic bath to ascertain the positive effects it imparts on the nitric acid and sulphuric acid leaching of spent silica-supported nickel hydrogenation catalysts. The extent of nickel recovered from ultrasound-assisted leaching was compared to that of the conventional mechanical stirring technique, whereby the actual ultrasonic densities of the ultrasound source were determined. Ultrasonic irradiation appreciably enhanced the extraction of nickel from the spent catalyst in all instances due to the physical and chemical effects of acoustic cavitation. In particular, sonication resulted in the expedited extraction of Ni, allowing a time reduction of 2 h in recovering ca. 70% Ni. Furthermore, it was also discovered that nitric acid was a more efficient leaching agent than sulphuric acid, achieving an improvement of ca. 20% in recovering Ni at 70 °C under ultrasonic conditions. Additionally, process optimisation was executed by adopting the response surface methodology, in which the modelled optimal conditions were ultrasonic bath amplitude = 67%, leaching temperature = 60 °C, nitric acid concentration 12.5 vol% and pulp density = 7.5%. Ultimately, the Ni recovery recorded under the optimal conditions was 99.37% in 2 h. Finally, an approximate economic analysis was performed to ascertain the recovery costs of nickel using the ultrasonic method. This study demonstrated the beneficial usage of ultrasound technology in the process intensification of hydrometallurgy, which could be employed on an industrial scale for higher recovery efficiencies and improved sustainability. [Display omitted] • Intensification of nickel recovery from spent catalysts via ultrasonic irradiation. • Physical and chemical effects of ultrasound both contribute to enhanced recovery. • Nitric acid as a leaching agent for nickel is more effective than sulphuric acid. • Nickel recovery of 99.37% obtained under optimised ultrasonic reaction conditions. • An efficient alternative to treat and recover hazardous metals from catalyst waste. [ABSTRACT FROM AUTHOR]

This present work investigates the novel method of synthesising copper manganese oxide (Hopcalite) catalysts with a Cu:Mn ratio of 1:2 by using a facile ultrasound-assisted co-precipitation synthesis technique. The CuMnO x catalysts were synthesised using an ultrasonic bath or an ultrasonic probe with varying ultrasonic powers. The catalysts were further characterised and evaluated for the oxidation of carbon monoxide (CO). Characterisation results revealed that samples prepared using the ultrasonic method exhibited enhanced physical properties, such as highly dispersed particles with a larger surface area and pore size. Besides, the presence of mixed copper and manganese oxide phases was detected, which provided synergistic interactions to facilitate and enhance CO oxidation. The amorphicity and reducibility of the catalysts were also improved, thus indicating the presence of more active sites. Furthermore, the catalyst prepared using the ultrasonic probe at a power of 23.3 W with a 15 min sonication time was found to be the most active, with the capability of oxidising CO to CO 2 to completion (100 %) at ambient conditions. It also possessed high catalytic stability, in which catalytic activity was not compromised for as long as 200 min. On the whole, this work has ascertained that by incorporating a simple ultrasonic irradiation step into the synthesis procedure of copper manganese oxide catalysts, the overall performance of the catalyst can be greatly improved compared to those already found in the literature, which demonstrates the potential application of this new method on a wider, commercial scale for carbon monoxide removal. • Copper Manganese Oxide synthesized in the presence of ultrasonication improved overall catalytic properties. • Mixed oxides of CuO, MnO2 and Cu2MnO4 were essential in the enhancement of copper manganese oxide catalytic activity. • Ultrasound synthesized copper manganese oxide showed complete removal of CO at ambient conditions. [ABSTRACT FROM AUTHOR]