You should be aware of fundamental differences between an oral presentation and a written report. In the presentation the listener by necessity has to follow the order the in which the speaker present his material. The reader of an article can skip parts, go back to the materials section, take a preview at the conclusions when he reads the results, etc. Exactly because of this reason, all scientific reports follow the generally adopted structure of Abstract – Introduction –Experimental Methods –Results – Discussion – Conclusions – References. However, this structure is totally UNSUITABLE for an oral presentation. Nevertheless, the majority of contributed talks at a conference adheres to it.
Why is this generally accepted structure unsuitable for lectures? Because the listener will have to remember details about the experimental methods until the results are presented, and he must recall the various results when the speaker deals with the discussion. In other words, details that should be combined (the why, how, what and what does it mean of a particular experiment) are treated separately. You ask a lot from the audience if they need to remember all these facts and figure until at the end you explain how these bits and pieces fit in a larger picture.
Grouping together what belongs together is a much better way to organize talk. Hence, if you discuss characterization by e.g. XPS, you start this part of the presentation with a few introductory remarks of what you want to learn about your catalyst, how XPS may help you to provide this information, when you show a few results and you discuss what they mean.
End with a conclusion. Then you go to the next item in your presentation, which may be determination of particle size by TEM. When finished with this, you may give an overall conclusion on the state of your catalyst before you go on to speak about catalytic behavior.