Catalytic nanosponges of acidic aluminosilicates for plastic degradation and CO2 to fuel conversion

The synthesis of solid acids with strong zeolite-like acidity and textural properties like amorphous aluminosilicates (ASAs) is still a challenge. In this work, we report the synthesis of amorphous “acidic aluminosilicates (AAS)”, which possesses Brønsted acidic sites like in zeolites and textural properties like ASAs. AAS catalyzes different reactions (styrene oxide ring-opening, vesidryl synthesis, Friedel−Crafts alkylation, jasminaldehyde synthesis, m-xylene isomerization, and cumene cracking) with better performance than state-of-the-art zeolites and amorphous aluminosilicates. Notably, AAS efficiently converts a range of waste plastics to hydrocarbons at significantly lower temperatures. A Cu-Zn-Al/AAS hybrid shows excellent performance for CO2 to fuel conversion with 79% selectivity for dimethyl ether. Conventional and DNP-enhanced solid-state NMR provides a molecular-level understanding of the distinctive Brønsted acidic sites of these materials. Due to their unique combination of strong acidity and accessibility, AAS will be a potential alternative to zeolites.

m-Xylene Isomerization. m-Xylene isomerization was carried out underflow condition (in HEL Auto-MATE reactor). The catalyst (200 mg) was hated to 300°C (ramping rate 2.5°C min -1 ) under a nitrogen flow of 5 mL min -1 . As soon as the temperature reached 300°C, the N2 flow was switched to m-xylene vapors (5 mL min -1 nitrogen flow bubbled through 15 mL m-xylene) and the products from the gas outlet was monitored by an Agilent 7890B GC-MS system. The catalytic performances after at least 90 min on stream were used for quantification.
Cumene (Isopropylbenzne) Cracking. The reaction was carried out underflow condition (in HEL Auto-MATE reactor), in which 200 mg of aluminosilicate was hated to 300°C (ramping rate 2.5°C min -1 ) under a nitrogen flow of 5 mL min -1 . As soon as the temperature reached 300°C, the gas flow was changed to cumene vapors (5 mL min -1 nitrogen flow bubbled through 12 mL cumene), and the products from the reactor outlet were monitored by an Agilent 7890B GC-MS system.

Synthesis of MFI-Meso-Zeolite.
Sodium aluminate (500 mg), NaOH (2 g), tetrapropylammonium bromide (7 g) and water (338 mL) were mixed at 600 rpm for 30 minutes. Acidity Quantification of AC*-1.9 by Catalyst Poisoning. Five powder samples of AC*-1.9 were treated with varying amounts of pyridine. For this, 200 mg of the AC*-1.9 was first degassed at 100°C for 2h to remove adsorbed moisture and cooled to 30°C under nitrogen flow. It was then treated with varying amounts of a freshly made stock solution of pyridine in dichloromethane (DCM). The mixture was then heated at 50°C under stirring for 30 min and then dried at 80°C in an oil bath to remove the DCM. The obtained dried powder was used for m-xylene isomerization reaction as per the above experimental conditions. m-Xylene conversion (%) was plotted against the amount (µmol/g) pyridine used to treat the AC*-1.9. The amount of the treated pyridine at which the conversion reached to zero was considered as the concentration of the acidic sites.

Ammonia Temperature Programmed Desorption (NH 3 -TPD) Study. The analysis was performed
using a flow-through microreactor system equipped with TCD (BELCAT Ⅱ). Around 50 mg of the sample was degassed at 120 °C for 1 h under He flow (50 mL min -1 ) and the temperature was reduced to 100 °C.
The activated sample was then exposed to 5% NH3 in Helium (30 mL min -1 ) at 100 °C for 30 minutes.
Then a fraction of the adsorbed NH3 was desorbed by passing the He (50 mL min -1 ) gas for 15 minutes.
From the start temperature (100 °C), the reactor was heated to 700 °C with a ramp of 10 °C /min under He flow of 30 mL min -1 .
Thermal Gravimetric Analysis of the AAS. The analysis was performed using a Mettler Toledo TGA instrument. The temperature program was kept exactly the same as that of TPD, except the gas used was nitrogen. In a typical analysis, 3-6 mg of sample was taken in an alumina crucible and was degassed at 120°C for 1 h under N2 flow (50 mL min -1 ). The temperature was then reduced to 100°C and gas flow was reduced to 30 mL min -1 , the system was stabilized for 45 minutes. From 100°C, the chamber was heated up to 700°C at the rate of 10°C min -1 under 30 mL min -1 N2 flow.
Pyridine adsorption study using DRIFT. This experiment was performed using a Jasco IR spectrometer equipped with PIKE DRIFT accessories. Approximately 10 mg sample was taken in a crucible and degassed to remove moisture at 450°C under a nitrogen flow of 10 mL min -1 for 1h in the DRIFT chamber.
Then the temperature was reduced to 50°C and pyridine vapor (using a flow of 10 mL min -1 N2) was passed through the sample chamber for 30 minutes. The weakly adsorbed pyridine was then removed by increasing the temperature to 120°C and 240°Cunder N2 flow of 20 mL min -1 for 1 h. DRIFT spectrum was then recorded at 120°C temperature with a resolution of 4 cm -1 .

Supplementary Figures
Supplementary Figure 1

Supplementary Tables
Supplementary Table 1