MICHELLE CASPER

Nanotechnology is the ability to control atoms to make the smallest possible objects. One area of research that is being greatly affected by nanoscience is the synthesis of catalysts. Catalysts are important in the production of chemicals. In fact, in 1998 they were used to make over $3 trillion in goods. Improving the activity and selectivity of catalysts would enhance production and benefit the industry. However, a better understanding of them is crucial to these endeavors.

The catalyst that I am making is bimetallic, because it is made of the metals platinum (Pt) and palladium (Pd). In order to make this catalyst, I must make a solution of Pt and a solution of Pd. To make the solutions I mix the salt, K₂PtCl₄, with water. Similarly,I make a Pd solution using K₂PdCl₄ salt.  I create both solutions so that they have the same concentration of metal ions. Then, in order to make the bimetallic catalyst, I mix the appropriate volume of each solution. For example, if I want to make a catalyst that is 75% Pt and 25% Pd, then I make 75% of the final volume be from the Pt solution and 25% of the final volume be from the Pd solution. I allow these solutions to mix, while bubbling Nitrogen (N₂) gas through it to get rid of O₂ that might be in the solution.

Next, I make the dendrimer solution by using an already manufactured fourth generation dendrimer (G₄-OH). The dendrimer is contained in a solution of methanol, which I remove by drying with a steady flow of N₂. Once the solution is dry (the weight of the solution stops decreasing because there is no more methanol that can leave, I dilute the dendrimer with water to the appropriate concentration. In the next step, I mix the Pt/Pd solution with the dendrimer and allow it to stir (with N₂ bubbling through to keep out air) for 3 days so that the metal atoms attach to the sites. After 3 days, reduce the dendrimer stabilized Pt/ Pd solution by adding NaBH₄, a reducing agent. Reducing the solution causes the metal atoms to clump together in the center of the dendrimer, forming a small particle, or nanoparticle.  Then, I perform a dialysis on the solution for 2 days.   After dialyzing the solution, I dry the Al₂O₃ support that will hold the nanoparticles. Heating the support, which is in the form of a white powder, at 300 Celsius for 4 hours removes all the water that may be present in the powder. This way, when I weigh 1 gram of the support in the next step, that weight will not include water.  I mix this one gram of support with the reduced dendrimer Pt/Pd solution and allow it to stir for 1 day so that all the nanoparticles will attach to the support. After one day, I filter out the extra water, collect the dry residue and crush it to obtain a powder with particles of uniform size. I heat this powder under Oxygen (O₂) gas at 300 Celsius for 3 hours and then under Hydrogen (H₂) gas at 300 Celsius for 3 hours. It is believed that the dendrimer is destroyed from the high temperatures, leaving the nanoparticles on the surface of the support. Together, the nanoparticles and support form a bimetallic catalyst.