High-performance perovskite oxides for acid-base catalysis are easily synthesized.

Chemical processes that are relevant to industry call for bifunctional acid-base catalysts. They enable synergistic and cooperative catalysis because they can simultaneously activate nucleophiles and electrophiles. Solid acid-base catalysts are particularly useful because they can be used again and again without producing waste.

However, it is challenging to control these catalysts’ structures for cooperatively workable active sites. Therefore, high-performance solid acid-base catalysts with desirable properties must be produced using straightforward and efficient methods.

A simple sol–gel method for the synthesis of highly pure bifunctional solid acid–base catalysts of perovskite-type oxides has been proposed by a group of researchers led by Professor Keigo Kamata from the Tokyo Institute of Technology (Tokyo Tech), Japan. This move pushes the boundaries of catalysis research. Their review was distributed in ACS Applied Materials and Connection points.

“Perovskite-type oxides are becoming increasingly important in a variety of fields, including magnetism, ferroelectricity, piezoelectricity, and catalysis.” Furthermore, the chemical composition of perovskite-type oxides can be used to adjust their structure and physiochemical properties.”

Professor Keigo Kamata from Tokyo Institute of Technology (Tokyo Tech), 

Prof. Kamata states, “Perovskite-type oxides are gaining importance in several fields, including magneticity, ferroelectricity, piezoelectricity, and catalysis,” providing an explanation for the selection of perovskite-type oxides. In addition, the chemical composition of perovskite-type oxides can be controlled to adjust their structure and physiochemical properties.”

Oxides of the perovskite type have a variety of compositions and exhibit high levels of structural stability, adaptability, and controllability for a variety of catalytic reactions. However, they have not been adequately investigated for corrosive base-catalyzed responses. Additionally, the current techniques for union are intricate, tedious, and require numerous means, making it challenging to orchestrate profoundly unadulterated and alluring perovskite oxide impetuses.

There are two essential steps in the team’s sol–gel method for overcoming these obstacles. Preparation of the precursor perovskite material is the first step, followed by a calcination procedure to increase the material’s surface area.

The researchers added malic acid and hydrogen peroxide to a metal alkoxide containing either titanium (Ti4+), zirconium (Zr4+), or niobium (Nb5+) cations to make the precursor. After that, they dried a metal acetate that contained an a-site element and added it to the solution, resulting in a powdered precursor.

Then, they exposed the forerunner to a calcination cycle by warming it to 550°C in a nitrogen environment and exposing it to air for 5 hours. The precursor’s surface area was increased as a result of crystallization caused by the high temperature and oxygen’s presence.

Of the different impetuses incorporated using this technique, the one with SrTiO3 nanoparticles (Sr: strontium) had the greatest amount of catalytic activity. Acetophenone was able to be effectively cyanosilylated with trimethylsilyl cyanide (TMSCN) under mild reaction conditions without having to undergo any thermal pretreatment.

The team discovered that the catalyst’s specific surface area of 46 m2/g was ten times greater than that of commercially available titanates (1–4 m2/g). Prof. Kamata adds, “We saw that the blended nanoparticles could enact TMSCN on the fundamental oxygen site and the carbonyl compound on the acidic Ti site. The high catalytic activity of the catalyst for the cyanosilylation reaction was due to this cooperative activation mechanism.”

In a nutshell, this straightforward strategy for producing catalytically useful, highly pure perovskite oxides has the potential to become a promising method for enabling reactions that only require mild conditions.

More information: Takeshi Aihara et al, Nanosized Ti-Based Perovskite Oxides as Acid–Base Bifunctional Catalysts for Cyanosilylation of Carbonyl Compounds, ACS Applied Materials & Interfaces (2023). DOI: 10.1021/acsami.3c01629

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