Evaluation of the acid–base properties of spent petroleum catalysts via the isopropanol probe reaction for potential reuse applications

Refinery spent hydroprocessing catalysts (SHCs) are metallic hazardous waste, the recycling of which is a serious environmental challenge. Herein, we studied the acid–base characteristics of SHCs using isopropanol (IPA) as a probe molecule to evaluate their possible reutilization in preparing the fresh catalyst support. The catalytic tests were conducted in a micro-fixed bed reactor at 175 °C for 3 h. An SHC sample of different forms such as coked (CSC), regenerated (RSC), and rejuvenated (RJSC) was evaluated for the test. They were characterized using different techniques, such as N2 physisorption, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The results show that all samples exhibited good IPA conversion (16.2 –30.7 mmol h−1 g−1) with propene being the main product (96-99%) formed. Among all samples, the RJSCs showed the highest IPA conversion rate (average 30.7 mmol h−1 g−1) followed by the RSCs (29.0 mmol h−1 g−1), and CSCs (16.2 mmol h−1 g−1) owing to its combination of the highest BET surface area (236.3 m2/g) and reasonable surface acidity. This work revealed that RJSCs pose suitable surface, textural, and thermal properties that could allow their reuse in fresh catalyst support, underscoring the feasibility of reuse strategies in catalyst synthesis.