Applied Catalysis B: Environmental, Vol.220, 9-18, 2018
PdIn intermetallic nanoparticles for the Hydrogenation of CO2 to Methanol
Direct hydrogenation of CO2 to methanol could offer significant environmental benefits, if efficient catalysts can be developed. Here, bimetallic Pd-In nanoparticles show good performance as catalysts for this reaction. Unsupported nanoparticles are synthesised by the thermal decomposition of Pd(acetate)2 and In(acetate)3 precursors in a high boiling point solvent (squalane), followed by reduction using dilute H-2 gas (210 degrees C). Adjusting the ratio of the two metallic precursors allow access to 5-10nm nanoparticles with different phase compositions, including metallic Pd(0), In2O3 and intermetallic Pdln. Liquid phase methanol synthesis experiments (50 bar, 210 degrees C, H-2:CO2 =3:1) identify the intermetallic Pdln nanoparticles as the most efficient. The catalysts exhibit around 70% higher methanol rates (normalised to the overall molar metal content) compared to the conventional heterogeneous Cu/ZnO/Al2O3 catalyst (900 and 540 p,mol mmol(PdlnorCuZnAl)(-1)h(-1), respectively). In addition, the optimum Pd/In catalyst shows an improved methanol selectivity over the whole temperature range studied (190-270 degrees C), reaching >80% selectivity at 270 degrees C, compared to only 45% for the reference Cu/ZnO/Al2O3 catalyst. Experiments showed an improvement in stability; the methanol production rate declined by 20% after 120 h run for the optimum Pdln-based compared with 30% for the Cu/ZnO/Al2O3 catalyst (after 25 h). The optimum catalyst consists of similar to 8 nm nanoparticles comprising a surface In-enriched Pdln intermetallic phase as characterised by XRD, HR-TEM, STEM-EDX and XPS. Post-catalysis analysis of the optimum catalyst shows that the same Pdln bimetallic phase is retained with only a slight increase in the nanoparticle size. (C) 2017 The Authors. Published by Elsevier B.V.
Keywords:Pdln catalysts;Pdln intermetallics;Nanoparticles;Methanol synthesis;CO2 hydrogenation;In2O3