The high silicon content in rice plant waste, specifically rice husks, makes this waste by-product attractive for the extraction and valorization of silicon oxide, which is widely used as an inert support in catalysis, drug delivery and molecular sieving. The procedures currently used for the treatment of plant biomass make extensive use of mineral acids (HCl, H₂SO₄, HNO₃), which, besides them being potential environmental pollutants, reduce the yield and worsen the chemical-physical properties of the product. In this study, an evaluation of the easy treatment of rice husks by benchmarking different, more eco-friendly carboxylic acids in order to obtain a mesoporous SiO₂ with an alveolar structure and a relatively high surface area and pore volume (300–420 m²/g, 0.37–0.46 cm³/g) is presented. The obtained mesoporous silicas are characterized by worm-like pores with a narrow size distribution and a maximum in the range of 3.4–3.5 nm. The mesoporous structure of the obtained materials was also confirmed by TEM. The complete removal of the organic part of the rice husks in the final materials was evidenced by thermogravimetric analysis. The high purity of the obtained mesoporous silica was detected using ICP analysis (98.8 wt. %). The structure peculiarities of the obtained mesoporous silicas were also characterized by solid-state NMR and ATR-FTIR spectroscopies. The morphology of the mesoporous silica was investigated by SEM.

The rapid expansion of the biodiesel industry has led to a significant surplus of crude glycerol, creating both a challenge and an opportunity for its sustainable valorization. The aim of this review is to provide a comprehensive overview of glycerol upgrading strategies that integrate upstream purification methods with downstream catalytic conversion pathways. Conventional and emerging purification technologies are critically discussed, with particular attention to their efficiency, cost, and compatibility with catalytic processes. Major catalytic routes such as acetalization, oligomerization, carbonation, hydrogenolysis, oxidation, etherification, esterification and steam reforming are systematically analyzed in terms of reaction mechanisms, catalyst design, and process conditions. Although high conversions and selectivities are often achieved under optimized conditions, key limitations such as catalyst deactivation, equilibrium constraints, feedstock impurities, and scalability issues remain significant barriers to industrial implementation. The review highlights the strong interdependence between glycerol purity, catalytic performance, and process design, emphasizing the need for integrated approaches. Recent advances in multifunctional catalysts, reactor engineering, and process intensification are discussed as promising strategies to overcome current challenges. Overall, this work provides a critical perspective on the state of the art and identifies future directions toward the development of efficient, scalable, and sustainable glycerol-based biorefinery processes.