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I wanted to decompose formic acid into $\ce{CO2}$ and $\ce{H2}$ for a school experiment. I was wondering what would be a suitable catalyst to use?

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In A Novel Example of Molecular Hydrogen Generation from Formic Acid at Visible-Light-Responsive Photocatalyst, the authors describe the formation of carbon dioxide and hydrogen from formic acid using visible light from a halogen lamp and freshly prepared $\ce{Cu2O}$ (or platinum-covered $\ce{Cu2O}$) as a catalyst.

The preparation of the $\ce{Cu2O}$ is described as follows:

Ten cubic centimeters of $\mathrm{1.0~mol~dm^{-3}}$ $\ce{CuSO4*9H2O}$ aqueous solution was dropped into $\mathrm{100~cm^3}$ of $\mathrm{1.0~mol~dm^{-3}}$ $\ce{Na2S2O3}$ aqueous solution, and subsequently, the mixture solution was dropped into $\mathrm{200~cm^3}$ of $\mathrm{1.0~mol~dm^{-3}}$ $\ce{NaOH}$ solution at 80 °C.

The resulting reddish-brown precipitate ($\ce{Cu2O}$) was separated by filtration and washed with deionized water, after which the precipitation was dried at 40 °C in an $\ce{Ar}$ atmosphere.

The conversion of formic acid is described as follows:

The photocatalytic experiment was conducted in a glass vessel (volume: $\mathrm{20~cm^3}$) containing $\mathrm{10~cm^3}$ of $\mathrm{2.5~mol~dm^{-3}}$ $\ce{HCOOH}$ and a known amount of photocatalyst (10 mg (ca. 70 μmol)) [...] in $\ce{Ar}$ atmosphere with stirring. The pH of the $\ce{HCOOH}$ solution was adjusted to 5.0 by the addition of $\ce{NaOH}$ solution.

A halogen lamp was used as the light source (light intensity: $\mathrm{280~mW~cm^{-2}}$ ) along with a sharp-cut filter (S76-L42, Suruga Seiki Co. Ltd.), using which the samples were irradiated with light of wavelength $\lambda > 420~\mathrm{nm}$. [...]

In summary, it seems possible to perform the experiment at school. UV filters are available from different manufacturers, a Schott N-WG320 might work.

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The wikipedia article of formic acid mention that decomposition of formic acid is carried out in the presence of acid, platinum or ruthenium catalyst.

Heat and especially acids cause formic acid to decompose to carbon monoxide (CO) and water (dehydration). Treatment of formic acid with sulfuric acid is a convenient laboratory source of CO.

In the presence of platinum, it decomposes with a release of hydrogen and carbon dioxide.

$$\ce{CH2O2 → H2 + CO2}$$

Soluble ruthenium catalysts are also effective(...)

For laboratory purposes, treating it with sulfuric acid is the best way.

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