Effect of the impregnation order on the nature of metal particles of bi-functional Pt/Pd-supported zeolite Beta materials and on their catalytic activity for the hydroisomerization of alkanes

Abstract

A series of mono-and bi-metallic (Pt and/or Pd) impregnated zeolite Beta samples have been prepared, characterized using a number of experimental techniques and catalytically tested for the hydroisomerization of a mixture of light paraffins. In particular, the effect of the order of Pt and Pd impregnation on the type/structure of the metallic species of the zeolite support and on the catalytic activity has been studied. Studied samples included a zeolite Beta in which both Pt and Pd (0.5 wt% of each) were simultaneously impregnated (and subsequently calcined and reduced) and two equally metal-loaded samples where the metals were sequentially impregnated (samples Pt*-Pd/Beta and Pd*-Pt/Beta, in which Pt and Pd were impregnated first, respectively). Mono-metallic samples were also prepared for comparison. TPR, DR-UV-visible, TEM, and XAS studies confirm that the order of impregnation plays a key role in the formation of metallic particles, influencing aspects as decisive in their catalytic behavior as their size, their dispersion and their composition (e.g., mono-or bi-metallic). The initial impregnation of Pd and subsequently of Pt produces a higher number of hetero-metallic (Pt-Pd) bonds than the simultaneous co-impregnation and especially for the impregnation in reverse order, which does not produce Pt-Pd bonds in a detectable amount. Based on the results from the different characterization techniques, a model of the metal distribution and composition of the particles was proposed for each bi-metallic sample. In good agreement, the order of the catalytic activity was found to be Pd*-Pt/Beta > Pd-Pt/Beta > Pt/Beta > Pt*-Pd/Beta > Pd/Beta, making clear that not only the presence of both metals, but also an adequate preparation method generating a high number of hetero-metallic bonds must be taken into account to improve the catalytic properties in relation to the mono-metallic samples.

Catalytic performances of dealuminated Hβ zeolite supported Pt catalysts doped with Cr in hydroisomerization of n-heptane

“…3 shows H 2 -TPR profiles for Cr/D␤, 0.4%Pt/D␤ and 5Cr0.4%Pt/D␤ catalysts. 0.4%Pt/D␤ displayed a hydrogen consumption peak at around 390 • C, indicating the strong interaction between Pt 2+ and ␤ zeolite with the formation of Pt-(O-Si ) 2−y y species, which are reduced at above 400 • C as described in previous literatures [34,35]. The slight difference of the reduction temperature should be relative to the dealumination of the Beta zeolite.…”

Waste to liquid fuels: potency, progress and challenges

“…When the reaction was conducted at 235 and 350 ° C for the two reactors at 1 MPa each, the gasoline range iso‐paraffins selectivity was stable at ~80% for 11 h. This property was attributed to the presence of Pd/HBEA in the lower reactor. Pd/HBEA catalyst had been previously reported as very active and selective for n‐paraffins upgrading into iso‐paraffins via isomerization . Similarly, the stability could be attributed to a balance between Pd sites and H‐BEA acidity , or the appropriate hydrogen partial pressure .…”

Sustainable Preparation of Supported Metal Nanoparticles and Their Applications in Catalysis

“…[46] Metallic Pt nanoparticles were found to be highly dispersed on the support (Figure 9), and their activities were comparable to those of silicoaluminophosphates and zeolites. [158,159] Metallic Pt nanoparticles have also been supported on magnetic nanoparticles through modification of Fe 3 O 4 with ionic liquid groups and subsequent ion-exchange of platinum salts (e.g. K 2 PtCl 4 ) with the linked groups and reduction of the Pt ions with hydrazine ( Figure 24) to give highly stable and active materials for the hydrogenation of alkynes and a,b-unsaturated aldehydes (Table 4).…”