Question

Please provide me a correct and clear answer for this question.

Why Mg/Al Hydrotalcite Catalyst is negligible toxicity and support the answer with references then show the advantages of the catalyst

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Answer 1

Explanation for negligible toxicity of Mg/Al hydrotalcite catalyst:

Availability of a heterogeneous catalyst, which contains cheap and abundant elements, has a scalable synthesis, is highly active and stable, retains its performance upon shaping into a technical form and can be operated in continuous mode, would pave the way for a more ecological and economical production of glycerol carbonate from glycerol and urea. Here, we show that a mixed oxide of Mg and Al is a promising active phase for this reaction. The solid comprises widely available and non-toxic metals, is easily obtained through the thermal decomposition of a hydrotalcite-like material and can almost match the product yield of state-of-the-art Zn-based catalysts, while displaying an outstanding resistance against leaching, which causes the rapid dissolution of the latter. In-depth characterisation uncovered that Lewis-basic centres are crucial to activate glycerol through dehydrogenation. Their concentration was maximised by optimising the composition and calcination temperature of the precursor, thus reaching up to 60% glycerol carbonate yield. Millimeter-sized extrudates featuring comparable basic properties to the powder sample, a well-developed meso- and macroporosity and high mechanical stability are obtained using a natural clay, bentonite, as a binder and thermally activating the hydrotalcite only after shaping. Upon testing in a continuous reactor under tuned conditions of temperature and pressure and in the presence of an aprotic solvent, the system attains the same glycerol yield as in the batch tests. During 100 h on stream, its activity decreases by 20% due to fouling, but can be fully restored upon burning-off of the carbonaceous deposits. This work discloses the development of a green material that exhibits high efficacy in a sustainable transformation, highlighting key parameters that should be generally taken into account in the design of an industrially relevant chemocatalytic technology.

Currently, interest has grown in finding effective solutions for the treatment of water pollution by toxic compounds. Some of the latter that have acquired importance are phenols and chlorophenols, due to their employment in the manufacture of pesticides, insecticides, cords of wood, paper industry, among others. The problem is rooted in that these compounds are very persistent in the environment because they are partially biodegradable and cannot be photodegraded directly by sunlight. Chlorophenols are extremely toxic, especially 2,4,6-trichlorophenol, which is potentially carcinogenic. In this work, Mg/Al-mixed oxide catalysts were obtained from the thermal treatment of hydrotalcite-type materials, synthesized by sol-gel method with different Mg/Al ratios. Hydrotalcites and Mg/Al-mixed oxides were physicochemically characterized by X-ray diffraction, thermal analysis (DTA and TGA), and N2 physisorption. The results were obtained on having proven the photocatalytic degradation of 2,4,6-trichlorophenol as a pollutant model by water. The catalysts obtained present the hydrotalcite phase with thermal evolution until achieving Mg/Al-mixed oxides at 500°C. The catalysts are of mesoporous materials and exhibiting large surface areas. The catalysts demonstrated good photocatalytic activity with good efficiency, reaching degradation percentages with Mg/Al = 1, 2, 4, 5, and 7 ratios of 94.2, 92.5, 86.2, 84.2, and 63.9%, respectively, until achieving mineralization.

Advantages of Mg/Al hydrotalcite catalyst:

There are many advantages to using hydrotalcites compared to other catalyst systems. Hydrotalcites are heterogeneous catalysts, improving the ease of catalyst separation after reaction. Furthermore, hydrotalcites are environmentally more benign (e.g. than heavy metals) and potentially cheaper.

Broadly speaking, there are three types of catalyst
systems for which hydrotalcites can be used:
• Redox catalyst. Various hydrotalcites, generally including copper or a heavy metal, are known
to be functional oxidation or reduction catalysts.
• Acid/Base catalyst. Our Mg/Al hydrotalcites have a unique and highly tunable structure with both acidic and basic properties. This bi-functionality allows for the use of these materials as catalysts for various organic conversions.
• Catalyst support. Hydrotalcites are known to be used as support for numerous catalytic species,
such as transition metals, alkali metals and even various anions.

Some more description about Hydrotalcite catalyst:

Hydrotalcites are layered double hydroxides (LDH) that contain positively charged hydroxide layers and charge balancing anions in the interlayer region. The hydrotalcites produced by our
proprietary technology are highly pure compounds of magnesium and aluminium with optional zinc. These products have significant anion-exchange capacity and behave as solid bases. The active base sites of hydrated hydrotalcite materials are mainly structural hydroxyl anions. Their basicity can be affected by structural and compositional parameters. For example, cations liks Zn or Ni give lower basicity than Mg. Less basic catalysts are also obtained from Cl-  or (SO ₄)^2-precursors than from (CO ₃)^2-containing materials. Another influence on the basicity is the Mg/Al ratio. When hydrotalcites are calcined (typically at 400-500 °C), mixed oxides are formed that have strong Lewis basic O2-Mn+ pairs.