Catalysis Science & Technology Blog

Pollutants enter the ecosystem through several pathways. Dangerous substances are released into the atmosphere in many ways, for instance by car exhausts, from industrial fumes and drainage effluents and through degradation of pesticides to name but a few.

A contaminant that appears to be ubiquitous and released through all these pathways is phenol. Phenols are highly toxic by inhalation, causing lung edema, through ingestion, damaging kindneys, brain and liver, and it is also an extreme irritant to the skin, causing severe burns. Some phenols are reported carcinogens.

Degrading and removing phenols from contaminated water is essential before allowing it to enter the ecosystem. Many techniques have been developed and applied in order to do this, such as the use of polymeric resins, microbial or enzymatic  degradation, adsorption and other catalytic chemical transformations.

A recently published work by Yao, Shi and Sui focused on the latter.

The group focused on the use of supported titania for the photocatalytic degradation of phenols under UV light in aqueous solutions. The catalyst was prepared by anchoring TiO2 onto fly ash deriving from municipal waste combustion: a less usual support compared to the more widespread silica, alumina and zeolites.

The fly ash was treated with acid, washed  and dried before the titanium oxide coating was applied as a sol-gel and the material calcinated. Several calcination temperatures were tested, finding that 500 °C provided the ideal condition to obtain high degree of crystallinity in the catalyst.

The catalytic loading was also explored in the range 10-30 g/L to determine the highest concentration achievable without preventing light from reaching the bulk of the solution; the catalyst also proved robust and reusable, retaining 90% of its photocatalytic activity even after 4 cycles. Several tests were peformed to ensure that the activity of the system was due to the photocatalyst, including test runs with untreated  fly ash, only titania and UV irradiation alone.

To better understand the characteristics of the system, a kinetic study of the degradation reaction was also performed, revealing a first order-like behaviour; also, a three-step mechanism for the fly ash-supported catalyst was proposed.

Using the optimal conditions found during the study, the group achieved  94 % of phenol degradation with a catalyst loading of 20 g/L over 4 hours of irradiation, which, with its reusability, could make the catalyst potentially employable for continuous use in water treatment.

Read more about this catalyst here.

Application of fly ash supported titanium dioxide for phenol photodegradation in aqueous solution

Zhongliang Shi, Shuhua Yao and Chengcheng Sui
Catal. Sci. Technol., 2011, Advance Article
DOI: 10.1039/C1CY00019E

It is a fact that the world’s reservoirs of conventional oil are diminishing at a fast pace, forcing mankind to look for alternatives – possibly cleaner, sustainable and more environmentally friendly than fossil fuels.

While the technologies to exploit renewable sources of energy, like wind, tidal or solar power, mature to the point of replacing old-fashioned sources of energy, the use of sustainable fuels may bridge the gap between us and a greener future.

Biodiesel, a mixture of methyl esters of fatty acids, is an alternative to normal diesel that burns producing consistently less greenhouse gases and sulphurated compounds. Biodiesel can be produced via trans-esterification of vegetable or animal oils with methanol generally under acidic conditions; however, the process is as yet not cost-competitive with conventional diesel fuel.

A way to reduce costs is to use cheaper oils, containing free, unesterified fatty acids in the production process introducing an extra esterification step in the process.

Lingaiah et al., in a recently published paper, presented their work on a solid-phase catalyst for the acidic conversion of fatty acids into their correspondent methyl esters that simultaneously catalyses trans-esterification, avoiding the need for a separate reaction.

To provide the necessary acidity, the group employed 12-tungstophosphoric acid (TPA), a heteropolyacid, supported on tin oxide to increase its thermal stability and to reduce catalyst leakage in the reaction media. A full study of the effect of parameters like TPA loading, reaction temperature, stirring speed and catalyst concentration resulted in and optimised TPA loading of 15 wt%  to provide ideal surface area and acidity.

The activity test were performed using palmitic acid as the model substrate at 65 °C with a total catalyst loading of 25%, in the presence of an excess of methanol (1:14) to improve conversion (since the esterification is a reversible reaction). After 4 hours, the palmitic acid conversion reached exceeded 70%, and tests showed the catalyst could be washed and reused 5 times without significant loss of activity.

To prove its industrial viability, simultaneous esterification/trans-esterfication in the presence of mixtures of triglycerides and free fatty acids was successfully performed.

Read the full paper here.

Efficient solid acid catalysts for esterification of free fatty acids with methanol for the production of biodiesel
K. Srilatha, Ch. Ramesh Kumar, B. L. A. Prabhavathi Devi, R. B. N. Prasad, P. S. Sai Prasad and N. Lingaiah
Catal. Sci. Technol., 2011, Advance Article
DOI: 10.1039/C1CY00085C, Paper