Cr‐modified MCM‐41 with different loadings were prepared and tested in the propane dehydrogenation (PDH) reaction. As for Cr/MCM‐41 system, the general knowledge was that high Cr loadings resulted in the reduction of silica surface hydroxyl groups, thus leading to the formation of inactive Cr(III) species, as clusters and/or crystalline Cr2O3. However, in the present work, isolated Cr(VI) states were identified in the Cr/MCM‐41 catalysts, instead of Cr(III) species, using UV‐vis and H2‐TPR. These isolated Cr(VI) species are difficult to reduce, causing the decreased activity for propane conversion and low selectivity towards C3H6 in the PDH process. In contrast, a good dispersion of the Cr species was obtained using a chromium column adsorption process, and the absence of the isolated state of Cr(VI) species on this sample contributed to high activity toward PDH process. The investigation of the isolated Cr(VI) species is very important for the Cr‐based PDH catalyst system.

The Cr/Al2O3 catalyst is a typical commercial catalyst system that has been widely applied for propane dehydrogenation (PDH). Appreciable improvement in catalytic performance of this catalyst is of importance regarding its further applications, but investigations of the interaction between Ce and Cr species and the effects of Ce modification on the dispersion and distribution of the active Cr phases have seldom been concerned in the previous works. In this work, M/Al2O3 (M: Cr, Ce, and Ce–Cr) catalysts were synthesized and the Ce-modified catalyst exhibited enhanced activity. It was shown that modification of Ce on the Cr/Al2O3 catalyst decreased the amount of inactive isolated Cr­(VI) sites. Meanwhile, the increased amount of oxygen vacancy was observed over the Ce–Cr/Al2O3 catalyst, which promoted the interaction between Ce and Cr species. The above results can be confirmed by the characterization results of X-ray diffraction, UV–vis, H2-temperature-programmed reduction, X-ray photoelectron spectroscopy, and Raman spectroscopy, which provide meaningful information for improving catalytic performance of the commercial Cr/Al2O3 catalyst during PDH.

Recycling waste Cr adsorbents as efficient catalysts reflects a new avenue of green chemistry and has important implications for environmental protection. In particular, the investigation of the effect of additional impurity ions is considered to be applicable for real Cr adsorbents. In the present work, reused Cr adsorbent syntheses from streams containing competing ions were developed for CH3SH abatment and propane dehydrogenation. Good dispersion of Cr species was obtained through this special procedure of preparation, and its difference from the traditional impregnation method was also examined. Furthermore, these reused Cr adsorbents with exposure to additional impurity ions provided different physicochemical properties, and different catalytic activities were shown accordingly. The results indicated that the impurity cations had little effect on the catalytic activity of the reused Cr adsorbents, while the impurity anions caused the destruction of the siliceous framework of the MCM-41 support and led to the formation of some inactive Cr­(VI) species, thus exhibiting decreased reactivity. Consequently, avoiding the addition of some anions was considered to be the premise for reusing the waste Cr adsorbents.

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This work designed a series of three-way catalysts (TWCs) with and without the modification by La 0.67 Fe 0.83 Cu 0.17 O 3 (LaFeCu) perovskite to reduce the formation of N 2 O and NH 3 emissions from natural gas vehicles (NGVs). The modified PtRh catalyst was found to have an efficient TWC performance and to reduce the formation of N 2 O and NH 3 significantly. The Xray diffraction and CO-Fourier transform infrared results demonstrated the formation of Rhx species, which would reduce the formation of NCO*, the main precursor of NH 3 . In situ diffuse reflectance infrared Fourier transform spectroscopy was used to confirm that no NCO* groups were found on the modified catalyst. The X-ray photoelectron spectroscopy results revealed the increase in the Pt 2+ content on the modified catalyst, promoting the decomposition of N 2 O. Also note that the modified catalyst produced far fewer N 2 O than the catalyst without modification in the model reaction of CO + NO. Our work would provide a solution to develop an advanced TWC for NGVs.