Shape Effect of Pd-Promoted Ga₂O₃ Nanocatalysts for Methanol Synthesis by CO₂ Hydrogenation

Abstract

In this paper, we present a new approach to investigate metal–support interaction in catalysis. First, we have carried out a controlled growth of two semiconductive Ga2O3 nanocrystals in distinctive shapes, namely, plate and rod with the majority of their surfaces covered with polar and nonpolar facets, respectively. We have then placed the same contents of Pd on these nanocrystals and carried out a systematic testing and characterization for methanol synthesis from CO2 hydrogenation under industrial applicable conditions. It is found that a low indexed (002) polar Ga2O3 surface is highly unstable, which gives oxygen defects and mobile electrons in the conduction band more readily than those nonpolar (111) and (110) surfaces. A significantly strong metal–support interaction between the (002) polar Ga2O3 surface and Pd was determined, and it gave rise to higher metal dispersion and facilitated electron transfer between them, leading to the formation of PdGa x . This renders such composite nanocatalysts active for methanol production.

Theoretical study of CO2 hydrogenation to methanol on isolated small Pd clusters

“…On the other hand, experimental results indicate that metallic Pd do not show any activity towards the direct conversion of CO 2 into methanol [21,22] . Moreover, as mentioned in the introduction, while many studies report that Pd island supported on metal oxides show good activity toward CO 2 hydrogenation to methanol, it is known that on such system the Pd island only acts as an H 2 dissociation site while the CO 2 /CO hydrogenations occurs on the oxides or Pd-oxides interface [12][13][14][15][16][17][18][19][20] . From these comparisons, it can be inferred that the usage of Pd in the form of small size cluster actually can enhance the catalytic performance of metallic Pd for CO 2 hydrogenation to methanol.…”

“…Pd island supported on metal oxides (Pd/Oxide) was reported to have good catalytic activities to convert CO 2 directly into methanol [12][13][14][15][16] . In this system, CO 2 adsorption and hydrogenation occurs at the metal-oxide surface [13,17,18] or at the Pd-oxide interface (forming Pd alloy) [18][19][20] . Meanwhile, due to its strong interaction with H 2 molecule, the Pd island only acts as a site for dissociating H 2 molecule and providing the dissociated H atoms to the oxide surface or to the Pd-oxide interface.…”

Polymorph selection towards photocatalytic gaseous CO2 hydrogenation

“…In the case of gas-phase heterogeneous hydrogenation of CO 2 to chemicals and fuels, performance optimization usually involves fine tuning the chemical and physical properties of the (photo)catalyst 1–3 . This can be achieved by doping 4,5 , isomorphous and aliovalent substitution 6,7 , size control 8,9 , morphology changes 10,11 , heterostructuring 12–14 , and support and promoter effects 15–17 .…”

CO2 hydrogenation to methanol: the structure–activity relationships of different catalyst systems

“…The colloidal catalyst was tested in liquidphase methanol synthesis and showed a fourfold increase in activity compared to Cu/ZnO/Al 2 O 3 and Pd/ZnO, comparable methanol selectivity, and high stability at 210°C and 50 bar. Qu et al (2014) prepared Pd supported on plate and rod Ga 2 O 3 nanocrystals. It was observed that Pd supported on plate nanocrystals resulted in higher Pd dispersion and stronger metal-support interaction compared to that of rod nanocrystals supported Pd.…”