Turnover Number Calculator

Inputs

Choose a mode for product formation, then enter catalyst amount. Add time to compute TOF.

Formula used

The turnover number is a dimensionless ratio of product formed per catalyst amount.

• TON = n_product / n_catalyst
• If time is provided: TOF = TON / t
• Mass to moles: n = m / M (with molar mass M)
• Concentration to moles: n = C × V (in mol/L and L)

How to use this calculator

1. Select a mode that matches your measurements.
2. Enter the catalyst amount and choose its unit.
3. Add molar mass if you use mass-based units.
4. Provide product data, or concentration-volume, or conversion.
5. Optionally enter time to compute turnover frequency.
6. Press Calculate to show results above the form.
7. Use the download buttons to save CSV or PDF.

Example data table

Technical article

1) Why turnover number matters

Turnover number (TON) describes how many product molecules a catalyst produces before it becomes inactive. Because TON is a ratio of moles, it allows fair comparisons across different reactor sizes, solvent volumes, and catalyst loadings. High TON values often indicate strong intrinsic stability under the chosen conditions.

2) Connecting TON to reaction yield

In practice, the numerator is the moles of the measured product. If selectivity is below 100%, using total converted substrate may overestimate TON. When you have analytical data, compute product moles from isolated yield, GC/LC calibration, or concentration-volume measurements so TON reflects the desired pathway.

3) Turnover frequency adds a time scale

TOF is defined as TON divided by reaction time and is commonly reported in s⁻¹ or h⁻¹. A catalyst can show high TON after long runs but modest TOF early on. Reporting both values clarifies whether performance is driven by fast kinetics, long lifetime, or both.

4) Moles conversion drives accuracy

This calculator accepts molar units, mass units with molar mass, and concentration-volume inputs. Small mass errors can propagate strongly when catalyst amounts are tiny. For example, a 5% weighing error on 2 mg catalyst changes TON by 5%. Always verify molar mass and unit prefixes (mmol, µmol, nmol).

5) Using conversion and stoichiometry safely

When only substrate conversion is available, product moles are estimated as n_substrate × conversion × stoichiometric coefficient. This method assumes known selectivity and product count per substrate. Set the coefficient to 2 when one substrate produces two product molecules, and document that assumption in reports.

6) Interpreting catalyst loading effects

At constant product amount, lowering catalyst moles increases TON, but it may also change the mechanism, induction period, or mass-transfer limits. For screening, keep conversions moderate and ensure mixing and temperature control. If TON rises as loading decreases, check for catalyst aggregation or deactivation at higher loadings.

7) Comparing catalysts across experiments

To compare catalysts fairly, standardize how product moles are measured and define the “active catalyst” basis. For supported or heterogeneous catalysts, moles of active metal sites may differ from total mass. If site counts are known, input catalyst moles on a site basis to obtain site-specific TON and TOF.

8) Reporting, uncertainty, and exports

Best practice is to report TON, TOF, time, temperature, concentration, and analytical method. Include uncertainty sources: weighing, calibration, and sampling. The CSV and PDF exports help capture inputs and computed values consistently, supporting lab notebooks and repeatability when you revisit conditions or scale up.

FAQs

1) Is turnover number dimensionless?

Yes. TON is the ratio of moles of product formed to moles of catalyst (or active sites). Because both are in moles, the units cancel and the result is dimensionless.

2) When should I report TOF instead of TON?

Use TOF when reaction time matters for comparing kinetics. TOF normalizes TON by time, highlighting how quickly a catalyst turns over. Report both when possible for a complete performance picture.

3) What catalyst amount should I use for heterogeneous catalysts?

Ideally use moles of active sites or accessible metal centers. If only bulk catalyst mass is known, convert using metal loading or site density estimates. Clearly state the basis in your report.

4) Why does my TON look unrealistically high?

Common causes are underestimating catalyst moles (wrong molar mass, unit prefix, or site basis) or overestimating product moles (assuming 100% selectivity). Recheck units, calibration, and whether product mass is pure.

5) Can I compute TON from concentration data?

Yes. Convert concentration to mol/L and multiply by solution volume in liters to obtain product moles. If concentration is in mg/L, you must provide molar mass to convert mass concentration into molar concentration.

6) Does TON depend on reaction time?

TON typically increases with time until catalyst deactivation or equilibrium limits further formation. Two experiments can have the same TON at different times. Adding time allows TOF calculation to distinguish fast from slow systems.

7) What time should I enter for TOF?

Use the effective reaction time during which product formation occurred under steady conditions. If there is a long induction period, you may report TOF using the active period and mention the induction separately for clarity.