Catalysis 2026 Issue

the metal component (gal- lium) acts as a dehydrogena- tion promoter, enhancing olefin aromatisation, while the acidic ZSM-5 framework catalyses oligomerisation and cracking reactions, leading to increased aromatic yields from biomass and plastics.11 Using the gas composition, it was speculated that the superior performance of the Zeopore-derived catalysts stems from the enhancement of both dehydrogenation and the cracking function via a proximity effect.12 , 13

250

Standard Zeopore/Ga

200

150

100

Figure 6 BTX yields obtained on extruded catalysts at the miniplant for PE (left) and 50/50 PE/biomass mixture (right). Yields normalised to Standard (=100)

and Ga appeared to specifically boost selectivity to valuable C₈ aromatics (see Figure 6 , left). For polyethylene (PE) mixed with biomass (Figure 6, right), the boost of aromatics was more equally spread over all BTX species. The differences between small-scale and miniplant can be attributed to dif- ferent reaction conditions, such as batch vs continuous setup, weight hourly space velocity (WHSV), and contact time. Increasing the efficiency of chemical conversions can have a significant and often overlooked impact on emissions Additional efforts were made to vary the reaction con- ditions to maximise the overall BTX yield for each catalyst. These efforts revealed that the Zeopore/Ga sample boosts the BTX level by 7 wt%. Importantly, this gain came at the expense of undesired gas formation, which was reduced by about 10% relative to the standard catalyst. Insights into reaction mechanism In the aromatisation of pyrolysis vapours using Ga/ZSM-5,

Enhancement of the external surface brings the zeolitic acid site closer to the dehydrogenation potential and hydro- gen transfer index (HTI) of the Ga sites. This significantly improves both the yield and selectivity of aromatics. This proximity effect is particularly pronounced for the Zeopore- derived Ga/zeolite, as the metal is introduced to the pure zeolite phase (Figure 3) and not to a mixed zeolite/binder phase, which would occur during the metal impregnation of a standard zeolite/alumina extrudate or pellet. The presence of a proximity effect in the Zeopore/Ga catalyst correlates well with its reduced gas make: the increased conversion of olefins to aromatics reduces the amount of olefins left in the gas phase, lowering the overall yield of gas and, concomitantly, leading to a more paraffinic gas composition (see Figure 7 ). The absence of butenes/ butanes (C₄s) from the Zeopore/Ga gas composition is striking and tentatively attributed to their higher reactivity compared to lower carbon numbers. The latter could, in turn, relate to the increased production of more alkylated C₈ aromatics. Impact on emissions Increasing the efficiency of chemical conversions can have a significant and often overlooked impact on emissions. A large number of byproducts are undesired, such as light hydrocarbons and non-condensable gases, especially methane. The latter are often flared or burnt off for heat recovery, that is, directly adding to the CO₂ footprint. By increasing selectivity to desired products, especially those not destined for fuels, emissions per ton of desired product can be sizably reduced.14 In the case of the Zeopore/Ga sample, not only was the overall gas production significantly lower, but the compo- sition of the gas (hydrogen + C1-C₄) was shifted towards lower carbon numbers and hydrogen. This meant that the relative abundance of carbon, hence potential CO2 , was significantly reduced. These two factors, combined with the increased BTX yield, imply that the selectivity-based CO2 emission per gram of BTX obtained is nearly halved. This reduction is an excellent indication of how catalyst design can help reduce emissions in future waste, CO2 , or biomass-based refineries.

Zeopore/Ga

Standard

Ethylene

Propane Propylene Ethane Methane

Figure 7 Weight-based gas composition obtained on extruded catalysts on the miniplant on PE

Catalysis 2026