Mesoporous Silica Supported Highly Dispersed GaN Catalysts Synthesized by Thermal Atomic Layer Deposition for Propane Dehydrogenation

As a typical wide band gap semiconductor material, gallium nitride (GaN) has found extensive applications in electronic related fields. This material could also make a promising catalyst. However, due to the difficulty of synthesizing high surface area GaN, its applications in catalysis have been greatly constrained. In this work, we report a novel method of synthesizing high surface area GaN catalysts supported on mesoporous silica (MCM-41) using thermal atomic layer deposition (ALD). Trimethyl gallium and ammonia were alternately dosed in the temperature range between 400-500 degrees C to generate nanoparticles of GaN on the support. Formation of highly dispersed GaN nanoparticles was confirmed and their structural and physiochemical properties were investigated. Structural characterization results reveal that amorphous GaN could be deposited on MCM-41 at 400 degrees C while crystalline GaN could only be formed at temperatures >= 500 degrees C and with multiple cycles of ALD. In propane dehydrogenation (PDH) reaction the ALD GaN/MCM-41 catalysts demonstrated excellent activity and selectivity. The specific activity of amorphous GaN turned out to be better than crystalline GaN, probably due to the larger fraction of active species exposed on the surface. Density function theory calculation was used to analyze the catalytic process and mechanism of PDH on supported GaN. It was revealed that GaN was active in the cleavage of C-H bond in propane. Amorphous GaN facilitates the adsorption of propane, which could also contribute to the enhanced activity of amorphous GaN.