Interplay between pore size and nanoparticle spatial distribution: Consequences for the stability of CuZn/SiO2 methanol synthesis catalysts

Abstract

Particle growth is a major deactivation mechanism for supported metal catalysts. This study reveals that the impact of pore size on catalyst stability is very sensitive to the nanoscale metal distribution. A set of ex-nitrate CuZn/SiO 2 catalysts was synthesised using SiO 2 -gel supports (pore size 5-23 nm). The catalyst compositions were adjusted to attain series of catalysts with either constant pore volumetric (1.6 Cu nm -3 ) or surface (2.0 Cu nm -2 ) overall metal loading. The procedures of thermal decomposition of the metal nitrate precursors were adjusted to achieve < 10 nm Cu particles displaying markedly different nanospatial distributions, i.e either gathered in high-metaldensity domains with small interparticle spacings or evenly distributed over the support with maximum interparticle spacings. Under industrially relevant methanol synthesis conditions, a strong increase of the deactivation rate with the support pore size is observed for catalysts with high-density domains of Cu particles. For these samples the local, nanoscale Cu surface loading is determined by pore size rather than by the overall metal content, as ascertained by HAADF-STEM/EDX.Conversely, Cu nanoparticles evenly spaced on the surface of the SiO 2 carrier show improved stability, being the deactivation rate chiefly independent of the support pore size. The differences in catalyst stability are ascribed to the dominance of different particle growth mechanisms. Our study highlights the significance of local, nanoscale properties for rationalizing the relevance of structural parameters such as pore size for catalyst stability.

Cu,Zn-based catalysts for methanol synthesis: On the effect of calcination conditions and the part of residual carbonates

“…On the other hand the copper content for AU is twice less as for To illustrate the long term deactivation dynamics of the catalysts the curves were extrapolated to 450 days TOS and compared with the recent literature results. There is an agreement of the processed data with the deactivation profiles of Fichtl et al [36] and Prieto et al [37] on the long term scale. However the discrepancies are significantly pronounced during the first 250 hours TOS (Fig 10).…”

“…For a comparison of the deactivation behaviour of the different catalysts, the relative activities a rel (t)=a(t)/a(0) were fitted with a simple Power-Law-Model according to da rel /dt = -k•a n as it was done in the literature previously [1,36,37]. Different deactivation orders n had to be used for the different catalyst families to result in a reasonable fit quality.…”

“…However the discrepancies are significantly pronounced during the first 250 hours TOS (Fig 10). The supported CuZn on SBA [37] catalysts undergo most rapid deactivation while the AU based catalysts tend to deactivate slower. The studied by Fichtl et al a highly active catalysts named FHI Standard [34] and other ZM derived catalyst have close relative loss of activity however the initial loss is considerably slower for the Al promoted FHI standard [42].…”

Towards ‘greener’ catalyst manufacture: Reduction of wastewater from the preparation of Cu/ZnO/Al2O3 methanol synthesis catalysts

“…H 2 -temperature-programmed reduction (H 2 -TPR) was performed on selected oxide catalysts as detailed elsewhere [25].…”

“…These include the combustion of organic metal salts [17,15,18,19], mechano-thermal [20], sol-gel [21,22] and colloidal synthesis [23]. In addition, low-metal-loading catalysts have been prepared by impregnation or chemical vapour deposition of Cu and Zn precursors on high surface area supports [24][25][26][27]. However, none of these methods has thus far been considered as a replacement for the classical co-precipitation route, which imparts an exclusive structure to the catalyst precursors, at both the meso-and nano-scales, as an essential requirement to achieve the complex and successful arrangement of the three metal components after catalyst activation [28].…”