In this work, the effect of surface properties of different alumina supports for CrO_x/Al₂O₃-catalysts on Cr-speciation and dehydrogenation activity was studied. For this purpose, a series of CrO_x/Al₂O₃-catalysts with a monolayer coverage of CrO_x (ca. 4.4 at. Cr/nm²) was prepared with γ-, δ-, (δ + θ)-, η-, θ-Al₂O₃ as supports. Systematic investigation of fresh catalysts with a set of techniques (chemical analysis, N₂ adsorption, XRD, Raman and ESR spectroscopy) showed that (i) chemical state distribution of Cr (Cr⁶⁺, Cr⁵⁺, Cr³⁺) was the same for all of the catalysts; (ii) CrO_x-species were in X-ray amorphous state; (iii) surface chromate species were virtually of the same oligomerization degree. However, aggregation of Cr³⁺ ions both in calcined and reduced catalysts is support-dependent. ESR data and infrared spectroscopic results of adsorbed CO showed that increase of Lewis acid sites (LAS) surface density on bare aluminas promotes the growth of the relative amount of Cr³⁺ ions in a relatively large Cr₂O₃-like clusters in the fresh catalysts. Catalytic testing in a cycling dehydrogenation-regeneration mode leads to catalyst deactivation. Investigation of spent catalysts revealed that deactivation is accompanied with sintering of Cr³⁺O_x-species with partial migration of Cr³⁺ ions inside alumina. It was observed that increase of LAS surface density on aluminas promotes the growth of both the initial dehydrogenation activity and stability upon cycling. On the basis of experimental results, it was concluded that (i) Cr³⁺ ions on the surface of relatively large Cr₂O₃-like clusters are more active than isolated and poorly agglomerated Cr³⁺ ions; (ii) increase in LAS concentration on alumina induces growth of surface coverage by Cr₂O₃-like clusters with concomitant modification of intrinsic activity of active sites through their interaction with support.

在这项工作中，研究了不同氧化铝载体对CrO _x / Al ₂ O ₃催化剂的表面性能对Cr形态和脱氢活性的影响。为此，制备了一系列具有单层覆盖CrO _x的CrO _x / Al ₂ O ₃催化剂（约4.4 at。Cr / nm ²），其中γ-，δ-，（δ+θ）-， η-，θ-Al系₂ ö ₃作为载体。使用一系列技术（化学分析，N ₂吸附，XRD，拉曼光谱和ESR光谱）对新鲜催化剂进行系统研究，结果显示：（i）Cr（Cr ⁶⁺，Cr所有催化剂的⁵⁺，Cr ³⁺）均相同。（ii）CrO _x物种处于X射线非晶态；（iii）表面铬酸盐种类实际上具有相同的低聚度。但是，在煅烧和还原的催化剂中Cr ³⁺离子的聚集都是依赖于载体的。ESR数据和吸附的CO的红外光谱结果表明，在相对较大的Cr ₂ O _3中，裸露氧化铝上路易斯酸位（LAS）表面密度的增加会促进Cr ³⁺离子相对量的增长。状的新鲜催化剂簇。在循环脱氢-再生模式下的催化测试导致催化剂失活。对废催化剂的研究表明，失活伴随着Cr ³⁺ O _x-物种的烧结以及氧化铝内部Cr ³⁺离子的部分迁移。观察到氧化铝上LAS表面密度的增加促进了初始脱氢活性和循环时稳定性的增长。根据实验结果，可以得出以下结论：（i）相对较大的Cr ₂ O ₃样团簇表面上的Cr ³⁺离子比孤立的且团聚性差的Cr ³⁺更具活性。离子 （ii）氧化铝上LAS浓度的增加导致Cr ₂ O ₃样簇的表面覆盖率增加，并伴随着活性位点与载体的相互作用而改变了活性位点的固有活性。