Investigating the Mechanism of Alkyne Hydrogenation through an Open-Ended, Inquiry-Based Undergraduate Research Project Exploring Heterogeneous Catalysis

Abstract

The catalytic hydrogenation of alkenes and alkynes is an important part of the undergraduate chemistry curriculum and is a fundamental process in chemical industry. Inquiry-based laboratory activities are presented that investigate the hydrogenation of alkynes on a nanoparticle palladium surface to form alkenes, which go on to form alkanes. Alkyne hydrogenation using H2 and/or D2 proceeds via a vinyl–palladium intermediate to form a π-bonded alkene–Pd species that can desorb or remain on the palladium surface and undergo further hydrogenation via the Horiuti–Polanyi mechanism, associated with extensive deuterium–hydrogen exchange. Central to the experiments is an inexpensive, easy-to-build glass tube containing palladium nanoparticles on alumina beads that can be used indefinitely. A total of seven inquiry-based questions are discussed regarding hydrogenation of alkynes. A similar number of open questions are discussed for further investigations by interested persons. These activities are suitable as guided research projects for science majors. Each experiment is performed by groups of two or three students in about an hour including analysis by mass spectrometry. An additional hour is allowed for student analysis and discussion of the mass spectral results, writeup, and future planning followed by about 30 min with the mentor for group presentation and discussion of the results. Results often lead to additional questions, either for clarification or for new exploration and form the basis for inquiry-based learning and problem-solving.

Microscale Catalytic Hydrogenation of Cyclopropane with Nanoparticle Palladium

“…Mass spectrometry is not useful for this study because cyclopropane and propene have the same formula and very similar mass spectral patterns. In our previous work with alkenes and alkynes, , deuterated π-bonded alkenes are observed when limited amounts of D 2 are used, establishing that alkenes can undergo D–H exchange and then leave the catalyst surface. With cyclopropane, propene is not observed.…”

“…Over the past decade we have published three related articles exploring the gas-phase hydrogenation and deuteration of alkenes, alkanes, and alkynes using short glass tubes containing 0.5% nanoparticle palladium on alumina. − These articles provided suitable open-ended activities for undergraduate research projects with opportunities for inquiry-based explorations that lead to conclusions about the possible reaction pathway. This article is similar in purpose and describes the hydrogenation and deuteration of cyclopropane, which takes place above 150 °C.…”

Electrochemical Ultrathin Metal‐Atomic Layer Deposition for Silica Microenvironment‐Assisted Cu‐Based Catalysis

“…These results affirmed the participation of amino-silica moieties in H-transfer and ruled out the classical mechanism of direct H-transfer from NH 3 ⋅BH 3 /CH 3 OH to alkyne exclusively by the metal surface. [43,44] To check the possibility of H/D exchange between the deuterated amines in EC-2DCu and CH 3 OH, we removed the deuterated catalyst after mixing it with CH 3 OH solvent for 2 h at 60 °C (under stirring) and introduced with the new non-deuterated catalyst. Upon successive hydrogenation of alkyne, no deuterium was incorporated in the alkene product (Figure S32, Supporting Information).…”

“…As a result, Cu-interfaced amino-silica showed distinct catalytic feature in contrast to the inactive bare Cu surface. In an advancement to the classical bare metal-surface hydrogenation reactions, [43,44] presently studied amino-silica microenvironment-assisted cooperative reaction mechanism is unprecedented in heterogeneous Cu-based hydrogenation reactions.…”

Developing a Catalysis Applied Research Community at a University of Applied Sciences: From Educational Setting to High-Quality Research Output

“…In recent years, several papers have been published also discussing the organization of an undergraduate research program. Often this undergraduate research is conducted by a dedicated research group within a university, in a course, or even a multiyear program for which only highly motivated students have been recruited. − These examples are beneficial for students who want to improve their research skills at an earlier stage of their academic career and are already motivated to follow a research career path. Some writers report programs which discuss undergraduate research programs dedicated to minority groups .…”