From powder to extrudate zeolite-based bifunctional hydroisomerization catalysts: on preserving zeolite integrity and optimizing Pt location

Abstract

The development of zeolite-based hydroisomerization catalysts in the powder form is widely spread in scientific literature but shaped bodies are the ones being employed in industry. This work aims at bridging that gap. The shaping procedure for HUSY zeolite in presence of an alumina binder disclosed herein achieved a full conservation of zeolite properties, e.g. porosity and Brønsted acidity. When Pt was located inside the zeolite and an homogeneous Pt distribution along the extrudate was ensured, shaped Pt-containing catalysts had similar hydroisomerization performances to those of powder Pt/zeolite in terms of turnover frequency per Brønsted acid site and maximal feed isomers yield. Conversely, non-uniform distribution of Pt along the extrudates diameter (macroscale) was observed to reduce the feed isomers yield. This was tentatively explained by the lower local metal to acid sites ratio in the core of the extrudates. Optimal performance of shaped bifunctional catalysts requires, hence, an adequate metal to acid sites ratio throughout the whole catalyst (i.e. at macroscale), even if full intimacy between catalytic functions is ensured at the nanoscale by the selective deposition of Pt inside the zeolite.

The Known and Overlooked Sides of Zeolite‐Extrudate Catalysts

“…Similar criterion also holds for the hydroisomerization of long chain nparaffins in some reports (e. g. isodewaxing for slack waxes). [44] However, a very recent report discloses a contractive principle for the catalyst design for the hydroisomerization of nheptane, whose alkene intermediate is relative "bulky" and prone to the cracking compared with its C 5 -C 6 counterparts. The exclusive deposition of Pt particles on γ-Al 2 O 3 binder (Pt-inbinder) results in a nanoscale intimacy between metal sites and active sites, which is beneficial for the catalytic activity and yield to the target branched isomers.…”

Hydroconversion of Perhydrophenanthrene over Bifunctional Pt/H‐USY Zeolite Catalyst

“…Commercial ultrastable Y zeolite powder (CBV with a Brønsted acid site concentration of μmol/g) from Zeolyst was shaped in extrudate using Pural SB-3 alumina binder provided by Sasol, according to a procedure described elsewhere. [27] An aqueous solution in a proportion of 62.5 g water per 100 g of dry powder, containing 6.50 g nitric acid per 100 g dry boehmite, was mixed with USY zeolite and boehmite powder, and stirred with a mixer for 30 minutes, at a frequency of 50 revolutions per minute. A solution composed of 64.5 g water per 100 g of dry powder, containing 2.5 g ammonium per 100 g of dry boehmite, was then added to the mixture, which was kneaded for 15 minutes, keeping the same frequency of stirring.…”

Deactivation and regeneration of Pt‐modified zeolite Beta–Bindzil extrudates in n‐hexane hydroisomerization

“…Metal–acid bifunctional catalysts are widely used in many industrially significant chemical processes, e.g. hydrocracking of heavy oils, dewaxing, reforming, selective ring opening and hydroisomerization 1–9 . Hydroisomerization of C 5 –C 6 n ‐alkanes involving three steps, namely dehydrogenation of alkanes, skeletal isomerization of olefins and hydrogenation of the latter, is one of the cheapest ways to improve fuel quality (increase in octane number) 3,4,9–11 .…”

“…Pt, Pd, Mo, W, Co, Ni), while isomerization or hydrocracking steps proceed on the acid sites (e.g. amorphous silica–alumina oxides, zeolites and mesoporous aluminosilicates) 1–3,5,9,12 …”

“…Diffusion of the olefinic intermediates between metallic and acidic sites is very important and therefore design of the metal–acid bifunctional catalysts plays a key role in the hydroisomerization of straight‐chain paraffins. The controlled acidity (Brønsted and Lewis) in terms of strength and the number of the acid sites, metal–acid balance and proximity between these two types of active sites should mainly be taken into account for optimal performance of bifunctional catalytic systems 2–5,8–10,12–17 …”