A size-selective method for increasing the performance of Pt supported on tungstated zirconia catalysts for alkane isomerization: a combined experimental and theoretical DFT study

Abstract

The trends in the development of acid catalysts for isomerization show that the diffusion and accessibility of products are more favored in mesoporous than in microporous materials. In this work,...

Unraveling the Effects of Fe and Mn Promoters on the Tungstated Zirconia Catalyst: A Dft Study

“…In order to determine the preferred binding site for Fe and Mn on the tungstated zirconia catalyst, one Fe(Mn) atom is added to the most stable WO 3 /ZrO 2 and (WO 3 ) 3 /ZrO 2 structures (which were previously determined in ref. 10). The incorporation of Fe or Mn is performed by including a single metal atom in every symmetrically non-equivalent site corresponding to a 1:1 and 1:3 metal:W ratio.…”

“…In the unpromoted catalyst the tungsten oxide clusters are reduced due to the charge transfer from the underlying support. The acquired charge in the trimer is larger than that in the monomer (-0.46 vs − 0.33 |e|) [10]. Upon the inclusion of the metals, WO x are further reduced.…”

“…The dopants slightly reduce the W atoms too. In addition, the number of unpaired electrons on the different structures evidence the presence of spin polarized states, unlike in the undoped WZ compounds, that have a closed-shell electronic structure [10]. The spin density of the most stable geometries is shown in Fig.…”

“…This charge redistribution capacity is intimately related to the domain size of the WO x nanostructures [5,9]. Recently, a novel alkoxidefree sol-gel method to synthesize mesoporous Pt/WO 3 -ZrO 2 catalysts, with a better control over the size of the WO x clusters, confirmed that polytungstates with an intermediate domain size provided the best activity in terms of the conversion and selectivity in the n-hexane hydroisomerization [10]. DFT calculations of model catalysts showed that the origin of such a size effect arises from a combination of two factors [10].…”

“…Recently, a novel alkoxidefree sol-gel method to synthesize mesoporous Pt/WO 3 -ZrO 2 catalysts, with a better control over the size of the WO x clusters, confirmed that polytungstates with an intermediate domain size provided the best activity in terms of the conversion and selectivity in the n-hexane hydroisomerization [10]. DFT calculations of model catalysts showed that the origin of such a size effect arises from a combination of two factors [10]. On the one hand, the reducibility and the Brønsted acid strength increases as the size of the WO x species increases.…”