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Catalysis Definitions and Calculation

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SiliaCat Heterogeneous Catalysts are sol-gel silica-supported catalysts that can be used to replace homogeneous catalysts.

Usually, heterogeneous catalysts supported on a silica matrix are immobilized by post-modification of the inorganic support. These supports, however, present a high degree of leaching due to the poor stability of the immobilized phase. With SiliaCat Heterogeneous Catalysts, the ligand is directly cross linked in an organic-inorganic framework. This results a high degree of stability of the catalysts. Compared to homogeneous catalysts, SiliaCat exhibits a good reactivity and selectivity with one of the major advantages being that the catalyst is eliminated from the reaction mixture by a simple filtration. Forget your purification problems with our SiliaCat catalysts family.

The process for using SiliaCat Heterogeneous Catalysts is outlined in the scheme below.

What is SiliaCat Heterogeneous Catalysts

 

Number of mol % of SiliaCat Catalysts

For each new experiment, we suggest using a molar percent of SiliaCat with respect to the substrate. This quantity has to then be optimized in order to obtain a good catalytic activity with the lowest consumption of the SiliaCat. For initial experiments we suggest to use an higher mol % of SiliaCat Catalyst in respect to the substrate and then decrease the quantity if yield and kinetics are already in line with your needs. During development applications work at SiliCycle, we always start using 1 mol % of catalyst.

 

Solvent

SiliaCat can safely be used in a wide range of organic and aqueous solvents commonly used in laboratory and in process work, such as DMF, DMSO, THF, ACN, alcohols, ethers, chlorinated solvents, water, etc. The nature of the solvent does sometimes influence the catalytic efficiency, however. If yield is low or kinetics are too slow, changing solvent or adding a co-solvent should be considered.

 

Solution Concentration

At low substrate concentration, the activity of the catalyst will be directly proportional to the number of moles of substrate available. If you increase the concentration of the substrate, the activity will increase until the active sites become saturated. So the substrate concentration is a parameter that needs to be optimized to develop your catalytic conditions.

 

Temperature

A catalyst's purpose is to enhance the kinetics of a reaction, so we recommend running the experiments at room temperature. In the optimization step, the temperature could be adjusted, if it is needed.

 

Reaction Time

In the case that the TOF is low, and increasing the temperature to increase the kinetics is not possible, we recommend increasing the contact time with the catalyst to complete the reaction. Also, in this case, increasing of the amount of catalyst is an option.

 

Turnover Number (TON)

In catalysis, the term turnover number has two meanings: the number of moles of substrate that a mole of catalyst can convert before becoming inactivated and is the amount of substrate converted per the amount of catalyst used.

In theory, the Ideal catalyst would have an infinite turnover number and would never be consumed. In practice, turnover numbers begin at 100 and can go up to a million, more so in some cases.

 

Turnover Frequency (TOF)

A catalyst’s turnover frequency number, or turnover number per time unit, characterizes its level of activity. So the TOF is the total number of moles transformed into the desired product by one mole of active site per hour. The larger the TOF, the more active the catalyst.

TOF = TON/hour

 

How to Calculate the Amount of SiliaCat Needed Based on Mol %?

One mol % (1 mol %) means 0.01 molar equivalent. If 3 mmol of the substrate is used, then 0.03 mmol of SiliaCat catalyst is required. To determine the weight of the catalyst needed, simply divide this value by the loading of the catalyst.

For example, SiliaCat DPP-Pd typical loading is 0.2 mmol/g, so 0.15 g is needed.

 

Solvent Molar Concentration

A 1.2 M solvent concentration means: 1.2 mmol of substrate per mL of solvent (or 1.2 mol of substrate per L of solvent)

Volume of solvent needed = mmol of substrate used
molar concentration desired

For example, if 3 mmol of the substrate is used, then, 2.5 mL of solvent is necessary to reach a 1.2 M concentration.

 

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  1. SiliaCat DPP-Pd Heterogeneous Catalyst (R390-100)

    SiliaCat DPP-Pd Heterogeneous Catalyst (R390-100)

    Typical Applications: Suzuki, Heck, Sonogashira, Kumada, Stille and Buchwald amination
  2. SiliaCat TEMPO Heterogeneous Catalysts (R723-100)

    SiliaCat TEMPO Heterogeneous Catalyst (R723-100)

    Typical Applications: Oxidation of alcohols or Aldehydes
  3. SiliaCat Pd0 Heterogeneous Catalysts (R815-100)

    SiliaCat Pd0 Heterogeneous Catalyst (R815-100)

    Typical Applications: Suzuki, Heck Sonogashira, Kumada, Stille, Selective debenzylation, Selective hydrogenation
  4. SiliaCat Pt0 Heterogeneous Catalyst (R820-100)

    SiliaCat Pt0 Heterogeneous Catalyst (R820-100)

    Typical Applications: Selective reduction of nitroarenes, Hydrosilylation
  5. SiliaCat complete heterogeneous catalysts kit (K305-100), including: SiliaCat DPP-Pd, SiliaCat Pd0, SiliaCat Pt0 and SiliaCat TEMPO

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