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Catalysis

Catalysis

The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.

Turnover Number and Catalytic Efficiency

Turnover Number and Catalytic Efficiency

The turnover number of an enzyme is the maximum number of substrate molecules it can transform per unit time. Turnover numbers for most enzymes range from 1 to 1000 molecules per second. Catalase has the known highest turnover number, capable of converting up to 2.8×106 molecules of hydrogen peroxide into water and oxygen per second. Lysozyme has the lowest known turnover number of half a molecule per second.
Chymotrypsin is a pancreatic enzyme that breaks down proteins during digestion....

Heterogeneous Catalysis

Heterogeneous Catalysis

Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...

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Related Experiment Video

Updated: May 6, 2026

Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation

Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation

Published on: July 18, 2017

Active and Stable PtPd Diesel Oxidation Catalysts under Industry-Defined Test Protocols.

Kang Rui Garrick Lim^1,2, Tanya Shirman^1,3, Todd J Toops⁴

¹John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, 02138, Massachusetts, United States.

|February 28, 2025

Summary

Aging a mixture of platinum (Pt) and palladium (Pd) catalysts creates an alloyed catalyst that enhances diesel oxidation and emission control. This novel approach improves hydrocarbon conversion and catalyst stability.

Keywords:

Alloys Catalyst stability Diesel oxidation catalyst Emission control Ostwald ripening Palladium Platinum

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Published on: May 22, 2020

Area of Science:

Catalysis
Materials Science
Environmental Science

Background:

Diesel fuel combustion produces CO and hydrocarbons, necessitating catalytic converters.
Platinum (Pt) and Palladium (Pd) nanoparticle catalysts are used but deactivate via sintering at high temperatures.
Vapor-mediated sintering of Pt is a major deactivation pathway.

Purpose of the Study:

To leverage vapor-mediated sintering of Pt to create a more active and stable diesel oxidation catalyst.
To investigate the formation and performance of an alloyed PtPd/Al2O3 catalyst.
To develop a practical method for producing enhanced diesel oxidation catalysts.

Main Methods:

Raspberry-colloid-templating (RCT) method to prepare Pt/Al2O3 and Pd/Al2O3 catalysts with partially embedded nanoparticles.
Aging a physical mixture of Pt/Al2O3 and Pd/Al2O3 catalysts at high temperatures.
Validation using an industry-defined emission control test protocol and X-ray photoelectron spectroscopy (XPS).

Main Results:

Aging the physical mixture formed an alloyed PtPd/Al2O3 catalyst that outperformed individual catalysts and the fresh mixture.
The aged alloyed catalyst demonstrated superior hydrocarbon conversion, stability, and resistance to sintering and SO2 poisoning.
XPS analysis showed increased metallic Pd content in the aged catalyst, correlating with enhanced activity.

Conclusions:

Vapor-mediated sintering can be advantageously utilized to form active PtPd alloy catalysts.
The RCT method provides a practical route to highly stable and active diesel oxidation catalysts.
This approach offers a promising solution for improving diesel emission control technologies.