Carbon-based solid acid catalysts were prepared using rice straw (RS) waste, and the effects of carbonization temperature and sulfonation temperature on the catalytic activity were investigated. The properties of the catalysts were characterized using thermo gravimetric (TG), scanning electron microscope (SEM), Brunauer–Emmet–Teller (BET), Fourier transform infrared spectroscopy (FT-IR), temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS), and their activities were investigated through the hydration of α-pinene. The conversion of α-pinene and the selectivity of α-terpineol reached 67.60% and 57.07% at 80 °C and atmospheric pressure in 24 h, respectively. The high catalytic capacity of the catalyst is attributed to the high acid site density and high porosity of the catalyst. TPD analysis and FT-IR spectroscopy showed that the catalyst produced by low-temperature carbonization at 300 °C followed by low-temperature sulfonation at 80 °C had abundant strong acid sites (0.82 mmol/g), which can effectively inhibit the side reactions of hydrated α-pinene. The total acidity reached 2.87 mmol/g. N₂-physisorption analysis clearly indicated that the obtained catalysts were mesopore-predominant materials, and the S_BET and V_Total of catalysts reached 420.9 m²/g and 4.048 cm³/g, respectively. Preparation of the catalyst involves low energy consumption, and its cheap raw materials make the whole process simple, economical, and environmentally friendly.

In this study, silicoaluminophosphate (SAPO)-34 and Me (Me = Cr, Co)-modified SAPO-34 were synthesized and used as catalysts to investigate the catalytic performance by means of a probe reaction from ethanol to ethylene. The metal oxides were loaded on the SAPO-34 support via an impregnation method. The synthesized catalysts were characterized using XRD, SEM, EDX, FT-IR, NH₃-TPD, BET, and TGA techniques. Compared to SAPO-34, SAPO-34 doped with metal oxides showed the same chabazite (CHA) topology. The structure and properties of the catalyst were further optimized by varying the amount of Me. The experimental results showed that Co-Cr/SAPO-34 exhibited the best catalytic performance when the reaction temperature reached 400 °C at a weight hourly space velocity (WHSV) of 3.5 h⁻¹, for which the single-pass conversion of ethanol was determined as 99.15%, and the selectivity of ethylene was 99.4% at an optimum catalytic performance in the reaction of up to 600 min. In addition, Co-Cr/SAPO-34 exhibited better catalytic activity and anti-coking ability than pure SAPO-34, which was attributed to its enhanced pore structure and moderate acidity. It can also be concluded from the results of this experiment that the performance of the Co-Cr bimetal-supported catalyst is better than that of the Cr mono-metal catalyst.

Using sodium lignosulfonate as feedstock, ZnCl₂ and NaHCO₃ co-activated the hierarchical porous carbons (HPCs) were prepared by one-pot pyrolysis with different NaHCO₃ dosages (0–4 g) and carbonization temperatures (400–600 °C). Subsequently, phosphotungstate (HPW) was supported with the resulting biochar for the α-pinene hydration reaction to produce α-terpineol. The optimum preparation conditions were determined according to the yield of α-terpineol. The formation mechanism and physicochemical properties of HPCs were analyzed through TG, SEM, XPS, XRD, FT-IR, and N₂ adsorption–desorption isotherms. The results demonstrated that NaHCO₃ underwent a two-step reaction which liberated a substantial quantity of CO₂, thereby enhancing activated carbon’s macroporous and mesoporous structures. Simultaneously, NaHCO₃ mitigated strong acid gas (HCl) emissions during ZnCl₂ activation. Compared with AC450-4:8:0 prepared by ZnCl₂ activation alone, the total pore volume of AC450-4:8:2 prepared by co-activation is increased from 0.595 mL/g to 0.754 mL/g and the mesopore rate from 47.7% to 77.8%, which is conducive to reducing the steric hindrance of the hydration reaction and improving the selectivity. Hydration experiments show that the selectivity of α-terpineol is 55.7% under HPW/AC450-4:8:2 catalysis, higher than 31.0% for HPW and 47.4% for HPW/AC450-4:8:0.

In the current investigation, carbon-based solid acid catalysts were synthesized from peanut shells (PSs) and rice straw (RS) using ZnCl₂ activation and concentrated sulfuric acid sulfonation. These catalysts were then employed for the hydration of pinene to produce terpineol. The research findings suggest that the natural porous structure of RS is more amenable to ZnCl₂ activation compared to PSs. Furthermore, the catalysts prepared from fully activated RS by ZnCl₂ (RSA-C-S) had a higher S_BET and higher density of oxygen-containing groups (–COOH) in comparison with unactivated RS-based solid acids (RSC-S). The characterization outcomes revealed that RSA-C-S possesses a specific surface area of 527.0 m²/g, significantly outperforming RSC-S, which has a surface area of 420.9 m²/g. Additionally, RSA-C-S registered a higher –COOH density of 1.37 mmol/g, as opposed to RSC-S’s, with 1.07 mmol/g, attributable to the partial oxidation of internal –OH groups during activation. Experimental data from hydration tests confirmed that the catalyst’s superior performance is largely attributed to its elevated specific surface area and a high density of –COOH functional groups. Under optimal reaction parameters, RSA-C-S demonstrated unparalleled catalytic efficiency in the synthesis of α-terpineol via hydration of α-pinene, achieving conversion and selectivity rates of 87.15% and 54.19%, respectively.

Copper(II)-containing aluminum phosphate material (CuAPO-5) was synthesized hydrothermally and used as a multiphase catalyst for the oxidation of α-pinene to verbenone. The catalysts were analyzed using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area techniques, X-ray photoelectron spectroscopy (XPS), and ammonia temperature programmed reduction (NH₃-TPD). Scanning electron microscopy (SEM), X-ray energy spectrometry (EDS), inductively coupled plasma emission spectroscopy (ICP-OES), Fourier infrared spectroscopy (FT-IR), and ultraviolet-visible spectroscopy (UV-vis) were performed to characterize the material. The effects of reaction temperature, reaction time, n(α-pinene)/n(TBHP), and solvent on the catalytic performance of CuAPO-5 were investigated. The results show that all the prepared catalysts have AFI topology and a large specific surface area. Copper is evenly distributed in the skeleton in a bivalent form. The introduction of copper increases the acid content of the catalyst. Under the optimized reaction conditions, 96.8% conversion of α-pinene and 46.4% selectivity to verbenone were achieved by CuAPO-5(0.06) molecular sieve within a reaction time of 12 h. CuAPO-5(0.06) can be recycled for five cycles without losing the conversion of α-pinene and the selectivity to verbenone.