Production of alkenes over chromia catalysts: Effect of potassium on reaction sites and mechanism

Jackson, S. David; Matheson, Isobel M.; Naeye, M.-L.; Stair, Peter C.; Sullivan, Vivian S.; Watson, Simon R.; Webb, G.

doi:10.1016/s0167-2991(00)80797-1

Cited by 5 publications

(10 citation statements)

References 3 publications

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“…On the basis of the characterisation results, the CrO x /alumina catalyst after reduction is similar to other chromia catalysts used for dehydrogenation reported in the literature [13,[16][17][18][19]21]. The amount of Cr(VI) found in the sample is consistent with the literature for similar catalysts [16][17][18][19] as is the absence of any XRD detectable crystalline chromium oxide.…”

Section: Cro X /Aluminasupporting

confidence: 85%

“…The amount of Cr(VI) found in the sample is consistent with the literature for similar catalysts [16][17][18][19] as is the absence of any XRD detectable crystalline chromium oxide. At this loading of chromia, a mixture of surface species such as dimers and polymers of various lengths have been shown to be present by Raman spectroscopy [21]. From the conversion data presented in Fig.…”

Section: Cro X /Aluminamentioning

confidence: 89%

“…The addition of potassium to catalysts is a standard method to change activity, change selectivity and reduce by-product formation [23]. Detailed spectroscopic and mechanistic analysis of CrO x /alumina has shown that the addition of potassium does not affect alkane dehydrogenation but significantly affects side reactions [21]. Therefore, the addition of potassium has a noticeable effect on product selectivity.…”

Section: K-cro X /Aluminamentioning

confidence: 99%

“…Most strikingly, no alkynes are formed over the K-CrO x /alumina, specifically 3-methylpentyne, which was a major product via structural isomerisation over CrO x /alumina. Much of this change can be understood as a neutralisation of the acid sites on the alumina; indeed, it has been shown in a number of reports that the role of potassium is to remove acid sites [20,21,24]. Nevertheless, there is still considerable alkylation with significant yields of iso-alkanes (including methylcyclohexane) although this could be base catalysed [25,26].…”

Section: K-cro X /Aluminamentioning

confidence: 99%

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Transhydrogenation of pentane and 1-hexyne over CrOx/Al2O3 and potassium-doped CrOx/Al2O3 catalysts

Garba

Jackson

2019

Appl Petrochem Res

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The transhydrogenation of pentane (P) and 1-hexyne (1HY) was investigated over 4% CrO x /Al 2 O 3 and potassium-doped 4% CrO x /Al 2 O 3 catalysts over a range of temperatures (523-773 K) with a 5:1 P:1HY ratio. Over the CrO x /Al 2 O 3 catalyst, transhydrogenation clearly occurred at temperatures below 625 K where the yield of alkenes was higher for the co-fed system than for a combination of the individual yields. Due to the acidic nature of the alumina, many of the products were alkylated olefins and alkylated hydrocarbons formed by coincident alkylation and isomerisation. When pentane was added to a feed containing 1-hexyne, the extent of carbon deposition was reduced. By comparing transhydrogenation to limited hydrogen 1-hexyne hydrogenation at 623 K, it was shown that the processes of hydrogenation and transhydrogenation were different, with hydrogenation favouring alkanes, while transhydrogenation favoured alkenes. This may be because pentane dehydrogenation only releases two hydrogen atoms, which only allows 1-hexyne to hydrogenate to 1-hexene. Therefore, if the rate of alkene isomerisation and desorption is faster than that of pentane dehydrogenation, only alkenes will be observed. The latter proposal would suggest that the dehydrogenation/hydrogenation process is closely coupled and would be consistent with pentane influencing 1-hexyne surface chemistry. The effect of the potassium doping was to increase the yield of alkenes. The reason for this may be related to changes in the nature of the surface chromia species. The potassium also neutralised the acid sites on the alumina, reducing the extent of alkylation and hydrogenolysis, which suppressed the formation of other alkynes in the product mix.

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Section: Cro X /Aluminasupporting

confidence: 85%

Section: Cro X /Aluminamentioning

confidence: 89%

Section: K-cro X /Aluminamentioning

confidence: 99%

Section: K-cro X /Aluminamentioning

confidence: 99%

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Transhydrogenation of pentane and 1-hexyne over CrOx/Al2O3 and potassium-doped CrOx/Al2O3 catalysts

Garba

Jackson

2019

Appl Petrochem Res

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“…However, the dopant has little direct effect on the trans-hydrogenation process rather it is used to remove and/or neutralize acid sites on a support such as alumina reducing catalyst deactivation [54]. It does not generally change the reaction mechanism [54,55].…”

Section: Role Of Dopantsmentioning

confidence: 99%

Catalytic upgrading of refinery cracked products by trans-hydrogenation: a review

Garba

Jackson

2016

Appl Petrochem Res

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The production of high premium fuel is an issue of priority to every refinery. The trans-hydrogenation process is devised to convert two low valued refinery cracked products to premium products; the conversion processes involve the combination of dehydrogenation and hydrogenation reaction as a single step process. The paper reviews the recent literature on the use of catalysts to convert low value refinery products (i.e. alkanes and alkynes or alkadienes) to alkenes (olefins) by trans-hydrogenation. Catalysts based on VO x , CrO x and Pt all supported on alumina have been used for the process. However, further studies are still required to ascertain the actual reaction mechanism, mitigating carbon deposition and catalyst deactivation, and the role of different catalysts to optimize the reaction desired products.

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Effects of potassium addition on the acidity and reducibility of chromia/alumina dehydrogenation catalysts

Rombi

Cutrufello

Solinas

et al. 2003

Applied Catalysis A: General

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Production of alkenes over chromia catalysts: Effect of potassium on reaction sites and mechanism

Cited by 5 publications

References 3 publications

Transhydrogenation of pentane and 1-hexyne over CrOx/Al2O3 and potassium-doped CrOx/Al2O3 catalysts

Transhydrogenation of pentane and 1-hexyne over CrOx/Al2O3 and potassium-doped CrOx/Al2O3 catalysts

Catalytic upgrading of refinery cracked products by trans-hydrogenation: a review

Effects of potassium addition on the acidity and reducibility of chromia/alumina dehydrogenation catalysts

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